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UNIT
D
Lightning flashes around
transmission lines
carrying electricity to
communities.
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The Characteristics
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Contents
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Static charges collect on surfaces and
remain there until given a path to escape.
10.1 Exploring the Nature of Static Electricity
10.2 The Transfer of Static Electric Charges
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10.3 Electrostatics in Our Lives
11
Current electricity is the continuous flow of
electrons in a closed circuit.
11.1 Current, Potential Difference, and Resistance
11.2 Series Circuits and Parallel Circuits
11.3 Ohm’s Law
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We can reduce our electrical energy
consumption and use renewable energy
resources to produce electrical energy.
12.1 Renewable and Non-Renewable Energy
Resources for Generating Electricity
12.2 Reducing Our Electrical Energy Consumption
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Unit Task
In your Unit Task, you will evaluate methods of local
electricity generation that could be used as backup
sources for the regional power grid. Your investigations
into the characteristics of electricity, methods of
conserving electrical energy, and methods of providing
electrical energy will help prepare you for your task.
Essential Question
How can we use local resources to generate electricity
in a dependable, environmentally friendly way?
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Exploring
Toronto was one of many cities that were without electricity during the 2003 blackout.
Some places in Ontario now celebrate Blackout Day on August 14 to remind people of
how important it is to conserve energy.
Blackout!
Electrical generating
stations from Ohio
to Ontario shut
down, leaving
50 million people
in the dark. Why?
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Imagine what it would be like to live in a world without
electricity. Now, count to nine. In a mere nine seconds, that
scenario came true. On August 14, 2003, at 4:11 in the afternoon,
50 million people in Ontario and the northeastern United States
were plunged into the largest electrical blackout in North
American history. Elevators stuck between floors, subways were
in blackness, traffic lights stopped working, and television screens
and computer monitors went dark.
Electricity is often generated far from cities and is distributed
along a network that includes electrical generating stations,
transmission lines, and distribution stations. This huge,
interconnected system of electricity networks is called the
“energy grid.” Ontario, New York, Michigan, and other
northeastern provinces and states are part of the eastern
interconnection grid.
Electricity cannot be stored for long after it is generated, so all
parts of the grid must maintain a balance of supply and demand.
If a transmission line or generator is overloaded, that part of the
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energy grid is disconnected automatically and the electricity is
sent along alternative paths. One cause of problems in an energy
grid is transmission lines that touch trees so that the electricity
moves through the trees into the ground instead of along the wire.
Preventing Future Blackouts
On August 14, a series of events, including human error, high
demand, lines touching trees, automatic shutdowns, and failures
of alarm systems, resulted in a huge surge of electricity in the
grid. Within seconds, 256 electrical generating stations from Ohio
to New York to Ontario shut down as a protective control. It took
almost two full days to get all the generating stations back in
operation and electricity restored to all the affected areas.
This blackout raised difficult questions that could only be
solved by government and electrical industry experts from both
Canada and the United States working together. How did the
blackout happen? What can be done to prevent such a blackout
from occurring again? These are very complex questions to
investigate.
By working cooperatively, groups from the two countries
successfully figured out the answers to these questions. Now,
because of their hard work, the electrical grid is safer and better
able to deal with a similar situation. Smaller, local blackouts do
occur from time to time. But the knowledge learned from the
mistakes of previous large blackouts helps reduce the chances of
such a large-scale blackout happening again.
D1
A transmission line is automatically
disconnected from the grid when it
touches treetops or other objects.
STSE Science, Technology, Society, and the Environment
Electricity Concept Map
Electrical energy is often in the news. You have
probably read or viewed reports about the costs
and benefits of producing energy from renewable
and non-renewable sources. You might be
practising some ways to reduce electrical energy
consumption and achieve electrical savings in
your home. And you can probably describe the
importance of electricity to your daily life.
Now is your opportunity to get a sense of how
your pieces of knowledge about electricity fit
together.
1. As a class, create a concept map about
electricity. Start with the word “electricity” in
the centre of a large piece of chart paper.
2. Add categories, terms, concepts, and
sketches to the map, making links between
the parts that are connected.
Exploring
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10
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Static charges collect on surfaces
and remain there until given a path
to escape.
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Skills You Will Use
In this chapter, you will:
Sparks flash from the centre of a plasma ball to the
point of contact where a hand touches the ball.
• investigate the transfer of static electric charges by friction,
contact, and induction
• predict the ability of different materials to hold or transfer
electric charges
• plan and carry out inquiries to determine and compare the
conductivity of various materials
• apply knowledge and understanding of the safe operation
of electrical equipment
Concepts You Will Learn
In this chapter, you will:
• learn about the differences between electrical insulators
and conductors
• explain how materials allow static charges to build up or to
discharge
• analyze the design of technological devices that improve
electrical efficiency or protect other devices by using or
controlling static electricity
Why It Is Important
Static electricity is part of our daily lives. By understanding
how charges build up and discharge, we can avoid problems
caused by sparks and make use of static electricity to
improve our lives.
Before Reading
Determining Importance
Preview the subheadings and illustrations in Chapter 10.
Which topics and illustrations are familiar? Which topics
and illustrations are unfamiliar based on your
background knowledge and experience? The unfamiliar
topics and illustrations represent the information that is
most important for you to learn. Create a list of learning
goals for this chapter based on the information that
represents new learning for you.
Key Terms
• conduction • conductor • electrical discharge
• electron • electron affinity • friction • induction
• insulator • static electricity
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10.1
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Exploring the Nature of Static Electricity
Here is a summary of what you
will learn in this section:
• Solid materials are charged by
the transfer of electrons.
• When an atom gains electrons,
it becomes negatively charged.
• When an atom loses electrons,
it becomes positively charged.
• Electrons can be removed from
objects through friction.
• Particles with unlike charges
attract each other, and
particles with like charges repel
each other.
• Electrical insulators and
conductors are materials
categorized by how freely they
allow electrons to move.
Figure 10.1 Electric charges cause strands of hair to repel each other and be attracted to the
balloon.
A Shocking Experience
On a cold winter day, you have probably pulled a sweater off over
your head or removed your hat and felt your hair flying up. Or
maybe you have reached to touch a doorknob or the door handle
of a car and received an electric shock. These examples and hairraising experiences like the one in Figure 10.1 are caused by
electric charges. Electric charges are charged particles that exert
an electric force on each other. These charged particles are very
small. In fact, there are millions of them on each standing hair in
the picture above.
The accumulation or gathering of even larger numbers of
electric charges can lead to some impressive electrical displays.
Think back to the last time you observed a lightning storm. The
large, bright flashes of lightning look like the small electric sparks
you may have seen when touching the doorknob or taking off
your sweater. In fact, they are the same thing, just different in
size. These are all examples of static electricity.
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D2 Quick Lab
Characteristics of Electric Charge
A characteristic is a distinguishing trait or quality of a
substance or object.
Purpose
To observe the characteristics of electric charge
Materials & Equipment
• confetti or gelatin powder
• plastic drinking straw
4. Turn one balloon so that its rubbed surface faces
away from the other balloon. Again bring the
balloons together. Record your observations for
steps 3 and 4.
5. If your classroom has a Van de Graaff generator,
your teacher will demonstrate the following
experiments by putting the materials for each
experiment in place and then turning on the
generator. Record your observations for each
experiment.
(a) Tape one end of the thin paper strips to the
Van de Graaff generator.
• 2 balloons
• Van de Graaff generator
(b) Place a stack of three aluminum pie plates on
the Van de Graaff generator.
• thin paper strips
• clear adhesive tape
(c) Place a clear plastic cup full of polystyrene
“popcorn” on the Van de Graaff generator.
Put a loose-fitting lid on top of the cup.
• 3 aluminum pie plates
• clear plastic cup with lid
(d) Attach a metal rod to a lab stand, and place it
close to the Van de Graaff generator.
• polystyrene “popcorn”
• metal rod and lab stand
6. Return everything you used to the areas
designated by your teacher.
Procedure
1. Read through the procedure steps, and make
predictions about what you think will happen in
each step. Record your predictions.
2. Sprinkle some confetti or gelatin powder in a
small area on your desk. Push a plastic drinking
straw through your hair several times, and bring it
close to the confetti or gelatin powder. Record
your observations.
3. Inflate two balloons, and knot the ends. Rub one
side of each balloon on your hair or clothing.
Hold the balloons by the knots, and bring the
rubbed surfaces slowly together. Observe the
results.
Questions
7. (a) Which objects were attracted to each other?
(b) Which objects were repelled or pushed away
from each other?
8. How did your observations compare with your
predictions for each step?
9. What do you think caused the movements that
you observed?
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Electrically Charged Particles
You may recall from earlier studies that an element is a pure
substance that cannot be broken down into simpler substances. An
element is made up of tiny particles called atoms. An atom is the
smallest part of an element with the element’s properties. Within
an atom, there are three types of smaller particles: protons,
neutrons, and electrons. Protons and electrons are electrically
charged particles. Protons have a positive electric charge (+), and
electrons have a negative electric charge (–). Neutrons have no
electric charge, so they are neutral. The protons and neutrons are in
the nucleus at the centre of the atom. The electrons are outside the
nucleus (Figure 10.2).
Although they contain electrically charged particles, atoms are
neutral. The number of protons in the nucleus equals the number
of electrons around the nucleus, so the number of positive and
negative charges is equal. This makes an atom neutral.
neutron
proton
nucleus
electron
Figure 10.2 Each atom is made up of protons and neutrons inside the nucleus and electrons
in the area around the nucleus.
Static Charges
W O R D S M AT T E R
“Static” is from the Greek word
statikos, meaning causing to stand.
The word “stationary,” which means
not moving, is based on the same
Greek word.
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Objects can become charged when electrons move from one object
to another. The electric charge that builds up on the surface of the
object is called a static charge or static electricity. The charges
are “static” because they remain very nearly fixed in one location
on the surface of the object until they are given a path to escape.
An object that has more electrons than protons is negatively
charged. An object that has more protons than electrons is
positively charged. You can group objects according to three kinds
of charge: positive, negative, and neutral. If a neutral object obtains
extra electrons, the object becomes negatively charged. If a neutral
object loses electrons, the object becomes positively charged.
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Friction and the Movement of Electrons
All solid materials are charged by the transfer of electrons. How
do atoms lose or gain electrons to become electrically charged?
One common cause of electron transfer is friction, which occurs
when objects rub against each other.
Friction is the force resisting the relative motion of two
surfaces in contact. When two objects rub together, the force of
friction can remove electrons from one object and cause them to
transfer to the other object. As one object loses electrons, the
other object gains them, as shown by the amber and fur in
Figure 10.4.
If you count the electrons in Figure 10.4, you will notice that
no electrons are lost during the process of charging. They are
simply transferred. The position of the positive charges does not
change during the process of charging.
W O R D S M AT T E R
“Electricity” comes from the Greek
word elektron, meaning amber, which
is fossilized tree resin (Figure 10.3).
Amber has been used for thousands
of years to study static electricity.
Figure 10.3 Amber is fossilized tree
resin. This piece of amber contains
bugs that were living on the tree and
got caught in the amber.
electrons
neutral
(a)
neutral
negative
(b)
positive
(c)
Figure 10.4 The amber and the fur are electrically neutral (a). If you rub the amber with the
fur, electrons transfer from the fur to the amber (b). As a result, the fur becomes positively
charged and the amber becomes negatively charged (c).
It’s important to remember that the transfer of the charges from
one object to another is possible because the two objects are
rubbing against each other. Both objects are neutral before they
are rubbed together. They become charged as a result of the
rubbing.
For any charging procedure, it’s important to keep in mind
that new electric charges are not being created. The electrons in
each object are just being rearranged within the object or
transferred to another object.
Static charges collect on surfaces and remain there until given a path to escape.
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Electron Affinity
Table 10.1 A Triboelectric Series
Tend to lose
Suggested Activity •
D3 Inquiry Activity on page 402
(+)
Different substances have different
electrons
human hands (dry)
abilities to hold on to electrons.
glass
The tendency of a substance to
human hair
hold on to the electrons is called
electron affinity.
nylon
Table 10.1 lists a series of
cat fur
selected materials in order of
silk
their electron affinity. You will
cotton
notice that the higher the material
steel
is in the list, the greater the
wood
tendency for that material to lose
electrons.
amber
This means that if you rub
ebonite
together two materials listed in
plastic wrap
Tend to
the table, you can determine
Teflon®
gain
which material will be positively
electrons
(–)
charged and which material will
be negatively charged. For
example, if you rub nylon and steel together, the nylon will
become positive and the steel will become negative. The nylon
will lose electrons, because it is higher in the table. The
electrons from the nylon are transferred to the steel, making
the steel negative.
This table is referred to as a “triboelectric” series. The term
comes from tribos, a Greek word meaning to rub.
Note that there can be a slightly different order for materials
such as fur or wood depending on which type of animal the fur is
from and which type of tree the wood is from.
Learning Checkpoint
1. Where are electrons in the atom?
2. What does “static” mean in “static electricity”?
3. What happens when two objects made out of different materials are
rubbed together?
4. What term describes an atom’s tendency to hold on to electrons?
5. In each of the following pairs, state which one is more likely to give up
electrons.
(a) wood or human hair
(b) plastic wrap or steel
(c) cotton or silk
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Laws of Attraction and Repulsion
During Reading
You may have heard the expression “opposites attract” in
discussions about people. This is definitely true for electric
charges (Figure 10.5). Scientists studying the interaction of
objects have observed that when a positively charged object is
brought close to a negatively charged object, the two objects
attract each other. When two objects with the same charge are
placed close together, the objects repel each other.
Visualizing and
Picture Mapping
Opposite charges attract.
Like charges repel.
Good readers use the strategy of
visualizing to understand the
important details of a large
amount of complex information.
One way to visualize is to create
a picture map. Using the
information about the laws of
attraction and repulsion, begin
drawing pictures to represent
the information provided in this
section. Add to your picture
map as you read about electrical
insulators and conductors.
Figure 10.5 If you increase the amount of
charge on objects, the attraction or
repulsion also increases.
As a result of many scientific investigations, scientists have
established the following laws of static electric charges.
• The law of attraction states that particles with opposite
charges attract each other.
• The law of repulsion states that particles with like charges
repel each other.
Coulombs
Charles-Augustin de Coulomb was a French physicist who
worked with electric charges and made several important
discoveries (Figure 10.6). He showed that when two charged
objects are placed closer together, the attraction or repulsion
increases. When the charged objects are moved farther apart,
the attraction or repulsion decreases. In his honour, the metric
unit for electric charge is named the coulomb (C). One
coulomb equals 6.24 × 1018 electrons added to or removed from
a neutral object.
Figure 10.6 Charles-Augustin de
Coulomb (1736–1806)
Static charges collect on surfaces and remain there until given a path to escape.
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Electrical Insulators and Conductors
Another way to group materials is by their conductivity.
Conductivity is the ability of materials to allow electrons to
move freely in them. Materials that hold onto their electrons and
do not allow them to move easily are called electrical insulators.
An electrical insulator is a solid, liquid, or gas that resists or
blocks the movement of electrons, as shown in Figure 10.7. Dry
wood, glass, and plastic are all examples of electrical insulators.
An insulator can hold a static charge because static charges
remain nearly fixed in place.
- +
++
+ +- - +
+
+- -+
+ +
+
- +-
(a) Insulator: The electrons (–) are bound
tightly to the nuclei (+) so they resist
movement.
-
+
+
+
+
-
+
+
+
+
- + - +
(b) Conductor: The electrons are not as
tightly bound to the nuclei. They can move
away from the nuclei.
Figure 10.7 Electrons in an insulator cannot move freely. Electrons in a conductor can.
Materials that allow electrons to change positions are called
conductors (Figure 10.8). Conduction is the movement or
transmission of electrons through a substance. Examples of
conductors include the metals copper and aluminum.
Some materials allow only some movement of electrons.
This is the category of materials called fair conductors. In a fair
conductor, the electrons do not move as freely as in a
conductor, but they are not held almost in place as they are in
an insulator.
Figure 10.8 The metal wire in the
electric fence allows electrons to
move. The plastic insulator resists the
movement of electrons.
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Table 10.2 gives some examples of conductors, fair conductors,
and insulators. There are variations within each category, as some
materials are better or poorer conductors than others.
Table 10.2 Conductivity of Selected Materials
Conductors
Fair Conductors
Insulators
copper
water with dissolved
minerals
rubber
aluminum
moist air
wood
iron
human body
plastic
mercury
carbon
pure water
other metals
soil
metal oxides, such as rust
Water as a Conductor
Notice in Table 10.2 that water is an insulator only if it is pure.
However, most water has dissolved minerals in it, so its
conductive properties change and it becomes a fair conductor.
This is why you do not want to be in a lake during a
thunderstorm. If lightning hits the water, the electric charges
from the lightning will spread out through the water and cause
you serious or fatal injury. This is also why you should not use
water to try to put out an electrical fire (Figure 10.9). You also
need to take care not to operate electrical appliances near water
or with wet hands.
Learning Checkpoint
Figure 10.9 Use an all-purpose fire
extinguisher for an electrical fire.
Take It Further
1. (a) What does the law of attraction state?
(b) What does the law of repulsion state?
2. What is a coulomb?
3. Define “electrical insulator.”
4. What does “conduction” mean?
A Faraday cage is an enclosure
made of conducting material that
protects its contents from electric
charges. Find out how airplanes,
cars, and even some specially
designed clothes can act as
Faraday cages. Start your research
at ScienceSource.
5. (a) Name two examples of good conductors.
(b) Name two examples of fair conductors.
(c) Name two examples of insulators.
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DI Key Activity
SKILLS YOU WILL USE
D3
Inquiry Activity
Skills Reference 2
Adapting or extending
procedures
Drawing conclusions
Investigating Static Electricity
Question
What is the effect of charged objects on each other
and on neutral objects?
Materials & Equipment
• 2 vinyl strips
• beaker
• clear adhesive tape
• watch glass
• ring stand
• wooden ruler or
metre stick
• paper towel
4. Bring one of the charged vinyl strips close to the
suspended acetate strip. Make sure the two strips
do not touch each other. Record your observations.
5. Place the beaker upside down on the desk or
table. Place the watch glass on top of the beaker
as shown in Figure 10.10. Balance the ruler so it
is lying flat and centred on the watch glass. Bring
a charged vinyl strip near, but not touching, one
end of the ruler. Record your observations.
• 2 acetate strips
Procedure
1. Copy the following table into your notebook to
record your findings. Give your table a title.
Hanging
Object
Approaching
Object
charged
vinyl
charged
vinyl
charged
acetate
charged
acetate
charged
acetate
charged
vinyl
ruler
charged
vinyl
ruler
charged
acetate
Predictions
Observations
Figure 10.10 Balance the ruler on the watch glass on top
of the beaker.
6. Bring a charged acetate strip near one end of the
ruler. Record your observations.
Analyzing and Interpreting
7. Usually, charged vinyl is negative and charged
acetate is positive. How does this information
explain your observations?
Skill Practice
2. Tape one end of a vinyl strip to the ring stand so
the strip hangs down. Rub the hanging vinyl strip
with the paper towel to charge it. Then, rub the
other vinyl strip with the paper towel, and bring
that vinyl strip close to the suspended strip.
Record your observations in your table.
3. Repeat step 2, using the two acetate strips and
the paper towel. Record your observations.
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8. Describe how you would modify the procedure in
this activity so that you could identify the type of
charge on a charged object.
Forming Conclusions
9. Write three statements that summarize your
observations.
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10.1 CHECK and REFLECT
Key Concept Review
1. (a) Draw a diagram of an atom that has
four protons, five neutrons, and four
electrons.
(b) Label each particle with its name and
whether it is positive (+), negative (–),
or neutral.
11. Copy this chart into your notebook. For
each pair, predict which substance becomes
more positively charged and which becomes
more negatively charged when the two
substances are rubbed together. Use
Table 10.1, A Triboelectric Series on
page 398, to help you make predictions.
Charged Pairs
2. (a) What is friction?
(b) Explain how friction can be used to
transfer electrons. Use two substances
from the triboelectric series in Table
10.1 on page 398 in your answer.
Pairs
cotton, silk
human hair,
human
hands (dry)
4. State the two laws of static electric charges.
Teflon®,
wood
5. Where are static charges held?
glass,
plastic wrap
7. (a) What is the difference between a
conductor and an insulator?
(b) What is an example of a conductor?
(c) What is an example of an insulator?
8. (a) What is the difference between a
conductor and a fair conductor?
(b) What is an example of a fair conductor?
9. Why can you not use water to put out an
electrical fire?
Becomes More
Negatively
Charged
cotton, steel
3. Explain why this statement is false: “A
neutral object contains no charge.”
6. Why might a plastic rod that contains a
large number of electrons not have a static
charge?
Becomes More
Positively
Charged
12. Make a list of five different ways in which
you experience static electricity in your
own life.
13. (a) While fishing in an aluminum boat in
the middle of a lake, you notice storm
clouds forming nearby. Why is it a good
idea to get to shore as fast as possible?
(b) Would your answer change if the lake
somehow became filled with distilled
water with no ions present in it?
Explain why or why not.
Reflection
Connect Your Understanding
10. Do two identical objects become statically
charged when you rub them together?
Explain why they do or do not.
14. What are two questions about static
electricity that you would like to explore
further?
For more questions, go to ScienceSource.
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The Transfer of Static Electric Charges
Here is a summary of what you
will learn in this section:
• Electroscopes are instruments
that detect static charge.
• In charging by contact, an
orginally neutral substance
gains the same charge as the
charged object that touched it.
• In charging by induction, an
originally neutral substance
gains the opposite charge to
the charged object.
• Neutral objects are attracted to
charged objects.
• Grounding an object transfers
electrons between the object
and the ground, making the
object neutral.
• An electrical discharge occurs
when charges are transferred
quickly.
Figure 10.11 The bits of paper are attracted to the statically charged comb.
Charged Objects
What does dust on a computer screen have in common with
paper on a comb (Figure 10.11)? In both examples, there is
attraction between objects with unlike charges. You may have
noticed a similar effect when you unpack a box containing
polystyrene packing foam and the little pieces of foam stick to
your skin and clothes. Polystyrene is very low on the triboelectric
series and becomes charged very easily.
How do you know when an object is charged? Rather than
testing whether the object sticks to something else, you can use
an electroscope, which is an instrument that can detect static
charge. The electroscope was first invented in 1748 by a French
clergyman and physicist named Jean Nollet.
A metal-leaf electroscope has two very thin metal pieces,
called leaves, suspended from a metal rod (Figure 10.12 on the
next page). The metal rod is attached to a top plate or metal knob.
When a charge is transferred to the plate or knob, the charges
spread out over the whole structure, including the leaves. The
greater the charge, the greater the separation between the leaves.
An electroscope is one of the devices that can be used to study
static electricity. The study of static electric charges is called
electrostatics.
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D4 Quick Lab
Using an Electroscope
Purpose
To determine what happens to an electroscope when
different charged objects are brought near it
4. Charge the glass, acrylic, or acetate rod by
rubbing it with the silk fabric. Repeat steps 2
and 3 using this charged rod.
Part 2 — Pith-Ball Electroscope
Materials & Equipment
• plastic comb or straw or ebonite rod
• metal-leaf and/or pith-ball electroscope
5. Charge the comb or straw by running it through
your hair, or rub an ebonite rod on a wool
sweater.
• glass, acrylic, or acetate rod
6. Bring the charged object near the pith ball but
do not touch it (Figure 10.13). Record your
observations.
• wool sweater
• silk fabric
7. This time, touch the pith ball with the charged
object. Then, touch it again. Record your
observations.
Procedure
Part 1 — Metal-Leaf Electroscope
1. Charge the comb or straw by running it through
your hair, or rub an ebonite rod on a wool sweater.
2. Bring the charged object near, but not touching,
the top of the electroscope (Figure 10.12).
Observe the motion of the metal leaves. Then,
move the object away and observe the leaves
again. Record your observations.
3. This time, touch the charged object to the top of
the electroscope. You can rub the object along
the top of the electroscope if necessary. Observe
the motion of the metal leaves. Then, move the
object away and observe the leaves again.
Record your observations.
Figure 10.12 Metal-leaf electroscope
8. Charge the glass, acrylic, or acetate rod by
rubbing it with the silk fabric. Repeat steps 6
and 7 using this charged rod.
Questions
9. What role did friction play in this activity?
10. With your group, explain what happened in Part
1, using your knowledge about charges. Assume
your object had a negative charge placed on it.
11. With your group, explain what happened in Part
2, using your knowledge about charges. Assume
your object had a negative charge placed on it.
Figure 10.13 Pith-ball electroscope
Static charges collect on surfaces and remain there until given a path to escape.
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Detecting Static Charge
In order to predict what charge is transferred to an electroscope,
you can use a standard set of charged objects, such as ebonite and
glass. Ebonite is a hard rubber material that is low on the
triboelectric series and readily accepts electrons. When ebonite is
rubbed with fur, it becomes negative (Figure 10.14). Glass is high
on the triboelectric series and tends to give away electrons. When
glass is rubbed with silk or plastic, it becomes positive, as shown in
Figure 10.14.
Figure 10.14 To test unknown charges, you can use the known charges on an ebonite rod (a)
and a glass rod (b).
Suggested Activity •
D5 Quick Lab on page 412
When a negatively charged rod is brought near a neutral
electroscope, the electrons in the electroscope are repelled by the
rod. The electrons move down into the leaves of the electroscope.
The leaves are now both negatively charged, so they repel each
other and move apart (Figure 10.15). When the negatively
charged rod is taken away, the negative charges in the
electroscope are no longer repelled, so they move throughout the
leaves, stem, and knob. The leaves drop down, and the
electroscope is neutral again.
–++–+
–
–+
+–
–+
–+
–+
++
+
–+
+
–
–+
–+
–+
–+
+
–+
–+
–+
– –
(a)
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+
–
–
+
–+
–
+
–+
– –
(b)
Figure 10.15 The leaves are
not separated in the neutral
electroscope (a). The leaves
repel each other when they
are charged negatively or
positively (b).
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Charging by Contact
During Reading
As you learned in section 10.1, electrons can be transferred
through friction. Electrons can also be transferred through
contact and conduction. You can charge a neutral object by
contact when you touch it with a charged object. Charging by
contact occurs when electrons transfer from the charged object
to the neutral object that it touches. The neutral object gains the
same type of charge as the object that touched it because the
electrons move from one object to the other (Figure 10.16).
+++
–+
–
–+
–
––+––+–+–
–+
–
–+
–
–+
–
+
+–
–+
+
+
(a)
Figure 10.16 (a) When a negatively
charged object touches a neutral object,
electrons move to the neutral object,
making it negative.
Understanding Terms
and Concepts
A Frayer quadrant can help you
understand a term or the
concept it represents. Divide a
rectangle into four sections, and
put the term or concept as the
rectangle’s title above it (e.g.,
Charging by Contact). In the top
left section, write a definition of
the term using your own words
and words from the text. In the
top right section, write facts
related to the term. In the lower
left section, write examples of
the term from the textbook. In
the lower right section, write
non-examples of the term.
(b)
(b) When a positively charged object touches
a neutral object, electrons move from the
neutral object to the positive object and make
the neutral object positive.
Suggested Activities •
• D6 Inquiry Activity on page 413
• D7 Inquiry Activity on page 414
Induction
Induction is the movement of electrons within a substance
caused by a nearby charged object, without direct contact
between the substance and the object.
If you rub a rubber balloon on your hair, electrons will
transfer from your hair to the balloon, making the balloon
negative. The charges stay in a nearly fixed, or static, position on
the balloon because rubber is an insulator. When you bring the
negatively charged balloon near a neutral wall, the negatively
charged electrons on the balloon repel the negative charges on the
wall, making that part of the wall a positive surface. The balloon
is said to induce a charge on the wall because it charges the wall
without contacting it (Figure 10.17).
–
+
–
+
–
–
+
–
+
–
+
–
–
–
+
–
+
–
+
–
–
+
–
+
–
–
+
–
+
+
+
+
+
–
–
+
–
–
–
+
–
–
–
+
–
–
–
+
Figure 10.17 The negatively charged
balloon has induced a positive charge
on the wall’s surface without touching
the wall.
Static charges collect on surfaces and remain there until given a path to escape.
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Charging by Induction
When you charge an object by induction, you use a charged object to
induce a charge in a neutral object and then ground the charged object
so it retains the charge. This newly charged object has the opposite
charge to the charge on the charging object. Grounding is the process
of connecting a charged object to Earth’s surface. When you connect a
charged object to the ground, you provide a path for charges to travel
to or from the ground. Figures 10.18 and 10.19 show the process of
charging by induction. Grounding occurs in diagram (b).
electrons
+++
+++ –
+
+
+ –
–
+
–
+
+
–
–
+
–
–
+
–
–
+
–
–
+
–
–
Figure 10.18 (a) When a negatively charged
object comes near a neutral
electroscope, it repels the
electrons in the neutral
electroscope.
–
–
– – –
–
–
++
–+
+
–
+
+
–
+
(b) When you ground the neutral
electroscope, you provide its
electrons with a path away from
the repulsive influence. Some
electrons leave the electroscope.
+
(c) When you remove the ground
and the charged object, the
electroscope is left with a
positive charge because it has
lost some electrons.
electrons
– –
–+–+–+
–++–+
–
–
–
– – –
– –
+
+
–
–––+
–
– –
– +
+
+
+
+
Figure 10.19 (a) When a positively charged
object comes near a neutral
electroscope, it attracts electrons
in the neutral electroscope.
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–
–
+
–
+
–
–
–
+
–
+
–
+
–
(b) When you ground the neutral
electroscope, you provide a path
for electrons to go toward the
positive influence.
–
– –
+
–
–
+
+
–
–
–+
+
–
–
(c) When you remove the ground
and the charged object, the
electroscope is left with a
negative charge because extra
electrons are trapped on it.
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Learning Checkpoint
1. What does an electroscope detect?
2. In the contact method of charging, what charge does a neutral substance
gain compared to the object that touched it?
3. In induction, what charge does a neutral substance gain compared to the
object brought near it?
4. What is the difference between charging by contact and charging by
induction in terms of electron transfer?
5. What is grounding?
Electrical Discharge
Once an object is charged, the charges are trapped on it until they
are given a path to escape. When electric charges are transferred
very quickly, the process is called an electrical discharge. Sparks
are an example of electrical discharge (Figure 10.20).
Have you walked across a carpet and reached for a doorknob
only to be shocked when you created a spark (Figure 10.21)?
When you shuffle your feet in slippers or socks on a carpet,
electrons are transferred through friction and you build up a
static charge. When your hand reaches toward the neutral
doorknob, the excess electrons transfer due to induction.
Figure 10.20 When a spark
occurs, the air becomes a passage
for the electrons to travel. Collisions
between moving electrons and air
particles release light and can also
make a crackling sound.
Transfer of charge
from girl to door
9G10.42
Transfer of charge
from carpet to girl
Figure 10.21 When electrons jump between your hand and a
doorknob, you can receive a surprising shock.
Static charges collect on surfaces and remain there until given a path to escape.
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Lightning
Lightning is an example of a very large electrical discharge caused
by induction. In a thunderstorm, a charged area, usually negative,
builds at the base of the cloud (Figure 10.22 (a)). The negative
charge at the base of the cloud creates a temporary positive area
on the ground through the induction process (Figure 10.22 (b)).
When enough charge has built up, a path of charged particles
forms (Figure 10.22 (c)). The cloud then discharges its excess
electrons along the temporary path to the ground, creating a huge
spark — lightning (Figure 10.22 (d)). This discharge creates a
rapid expansion of the air around it, causing the sound of
thunder.
electrons
(a)
(b)
(c)
electrons
(d)
Figure 10.22 Lightning is an atmospheric discharge of electricity.
It is interesting to note that air is normally an insulator. If it
were not, lightning would occur every time that clouds formed.
For lighting to occur, charges in the clouds must build up to the
point where the air cannot keep the charges separated from the
ground. At this point, the air stops being an insulator and
becomes a fair conductor, resulting in a lightning strike.
Earth is a donator or receiver of charge and is so large that
overall it is not affected by the electron transfer of huge lightning
strikes. As a result, the ground is always considered neutral.
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Electrostatic Generators
Take It Further
Scientists use several devices in the laboratory to study how static
charges create lightning and other phenomena, such as the static
that affects clothes coming out of the dryer.
Early electrostatic generators were called “friction machines”
because they used direct contact between different surfaces to
create charged areas. A glass sphere or cylinder was rubbed
mechanically by a pad to charge it up.
More recent machines, such as the Van de Graaff generator,
create charge through friction between the roller and belt and
then transfer the charge to a large metal sphere, as shown in
Figure 10.23.
Sometimes, lightning strikes start
from the ground and go to a
cloud. There are also cloud-tocloud lightning strikes. Find out
more about different types of
lightning. Create a visual display of
your findings. Use ScienceSource
as a starting point.
charge collector
metal sphere
Teflon™ roller
rubber belt
insulating support
nylon roller
motor-driven
pulley
Figure 10.23 (b) The static charge on a Van de Graaff generator
has a hair-raising effect on these students.
comb
Figure 10.23 (a) This Van de Graaff generator is set up so its dome
is negatively charged. A Van de Graaff generator can also be
charged positively by using different roller materials.
A Wimshurst machine creates charges on two slowly
rotating disks with metal strips placed around the disks
(Figure 10.24). The charge is built up using induction
between the front and back plates as the disks turn in
opposite directions. The excess charge is collected by
metal combs with points near the turning disks.
Figure 10.24 The Wimshurst machine uses
induction to build up charge and create sparks.
Static charges collect on surfaces and remain there until given a path to escape.
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D5 Quick Lab
Charge Sorter
Materials that tend to lose electrons are higher on a
triboelectric series. Materials that tend to gain
electrons are lower on a triboelectric series.
Purpose
4. Use a charged ebonite rod to test the charge on
the electroscope by bringing it near the knob.
Do not touch the rod to the electroscope
(Figure 10.25). Observe the motion of the leaves.
5. Record the charge of material A.
To sort materials based on their ability to hold on to
static charge
Materials & Equipment
• materials such as fur, silk, aluminum, paper towel,
leather, wood, amber, hard rubber, Styrofoam®,
plastic wrap, vinyl (PVC) and Teflon®
• metal-leaf electroscope
• known charged object, such as an ebonite rod
rubbed on fur to create a negative charge
6. Ground the electroscope by touching it with
your hand. Then, charge the electroscope
using material B.
7. Use a charged ebonite rod to test the charge on
the electroscope by bringing it near the knob.
Do not touch the rod to the electroscope.
Observe the motion of the leaves.
8. Record the charge of material B.
9. Repeat steps 3–8 for each pair of materials.
CAUTION: Some people are allergic to fur.
Questions
10. Which materials were good electron receivers
and would appear lower on a triboelectric series?
Procedure
1. Make a table like the one below to list your
materials, predictions, and results. Give your
chart a title. Record your predictions.
Materials
Prediction
of Charge
A
B
A
1.
fur
silk
2.
fur
aluminum
3.
silk
aluminum
4.
silk
paper
B
Actual
Charge
A
11. Which materials were good electron donors and
would appear higher on a triboelectric series?
12. Create a triboelectric series by listing the
materials you used in order, according to their
electron affinity.
B
2.
Record your predictions for what charge each
material in each pair will have when the
materials are rubbed together.
3. Rub together the first pair of materials, A and B.
Then, touch material A to the knob of the
electroscope to charge the electroscope.
Figure 10.25 To test the charge on the electroscope, bring the
charged ebonite rod near it. Do not touch it.
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SKILLS YOU WILL USE
D6
Inquiry Activity
Skills Reference 2
Making predictions
Observing, and recording
observations
Charging by Contact
Question
What charge does the electroscope gain compared to
the charging rod?
5. Charge the glass rod by rubbing it with silk. Bring
the glass rod near, but not touching, the top of
the electroscope. Record your observations using
a labelled diagram.
Materials & Equipment
• ebonite rod
• glass rod
• fur
• silk
6. Touch the top of the electroscope with your hand.
Trial B
• metal-leaf electroscope
7. Repeat steps 2–4 using a glass rod charged with
silk. Use a charged ebonite rod in steps 5. Repeat
step 6.
CAUTION: Some people are allergic to fur.
Procedure
1. Make a table like the following to record your
predictions and observations. Give your table a
title. Record your predictions.
Motion of Leaves
Trial
Trial A
Predictions
Observations
8. Return all materials to the areas designated by
your teacher.
Analyzing and Interpreting
9. (a) Explain why the leaves moved when the
ebonite rod touched the electroscope in step 3.
(b) What charge was left on the electroscope?
10. (a) Explain why the leaves moved when the glass
rod touched the electroscope in step 5.
ebonite rod
touching
ebonite rod
near
(b) What charge was left on the electroscope?
11. How do your predictions compare with your
observations?
glass rod
near
Trial B
4. Rub the ebonite rod with the fur again. Bring it
near, but not touching, the top of the
electroscope. Record your observations using a
labelled diagram.
12. In terms of charge movement, explain in words
and diagrams the effect of:
glass rod
touching
(a) an identically charged rod near the electroscope
glass rod
near
(b) an oppositely charged rod near the electroscope
ebonite rod
near
Skill Practice
13. Explain how you would find the charge of an
unknown material.
Trial A
2. Charge the ebonite rod by rubbing it with the fur.
Forming Conclusions
3. Brush the ebonite rod against the top of the
electroscope. Record your observations of the
electroscope leaves using a labelled diagram.
14. Write a summary statement about the charge the
electroscope gains and the charge of the
influencing rod.
Static charges collect on surfaces and remain there until given a path to escape.
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SKILLS YOU WILL USE
D7
Inquiry Activity
Skills Reference 2
Charging by Induction
Question
What charge does the electroscope get compared to
the charging rod?
Gathering, organizing, and
recording relevant data from
inquiries
Interpreting data/information to
identify patterns or relationships
4. Remove your hand from the electroscope, and
then move the ebonite rod away. Observe what
happens to the leaves of the electroscope.
Record your observations.
5. Bring a charged ebonite rod near the electroscope.
Record what happens to the electroscope leaves.
Materials & Equipment
6. Bring a charged glass rod near the electroscope.
Record what happens to the electroscope leaves.
• ebonite rod
• fur
• glass rod
• metal-leaf
electroscope
• silk
7. Repeat steps 2–5 except start by charging a glass
rod against silk in step 2. Use a charged ebonite
rod for step 6.
CAUTION: Some people are allergic to fur.
Procedure
Analyzing and Interpreting
1. Make a table like the following. Give your table a
title. Record your predictions.
Motion of Leaves
Trial
Trial A
Predictions
ebonite rod
away
glass rod
near
glass rod
away
glass rod
near
ebonite rod
near
Trial A
2. Charge the ebonite rod by rubbing it against the
fur.
3. Bring the ebonite rod near the electroscope. Be
careful not to touch the rod to the electroscope.
While you hold the rod there, touch the top of the
electroscope with your hand.
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The Characteristics of Electricity
8. (a) Compared to the original rod that was brought
near the electroscope, what charge did the
electroscope end up with?
(b) How do you know?
Observations
ebonite rod
near
Trial B
Trial B
9. Explain what happens to the electrons in the
electroscope when your hand touches the
electroscope.
10. (a) Why did you have to remove your hand first
before you moved the rod away?
(b) What would have happened if you had moved
the rod away and then your hand?
Skill Practice
11. How else could you ground the electroscope?
Forming Conclusions
12. Summarize the method of charging by induction
by using diagrams labelled with the motions of
charges.
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10.2 CHECK and REFLECT
Key Concept Review
1. How are lightning and a spark similar?
2. (a) How do objects become negatively
charged using the contact method?
(b) How do objects become positively
charged using the contact method?
3. Explain how a substance becomes
temporarily charged by induction when a
charged object is brought near.
8. (a) Why do the leaves of the charged
electroscope shown below move farther
apart if a rod with the same charge is
brought near?
(b) Why would the leaves move closer
together if the rod had the opposite
charge to the electroscope?
+
+
+
4. Explain how to charge an object
permanently using induction.
5. Using a sequence of labelled diagrams,
explain how a positive balloon will stick to
a neutral wall. Under each diagram,
describe the motion of the charges.
+
+
+
+
Connect Your Understanding
Question 8
6. (a) How does the process of grounding
occur when you receive a spark from
touching a metal shopping cart?
(b) How does the process of grounding
occur during a lightning strike?
7. What would change about the way an
electroscope worked if its metal knob were
replaced with a plastic knob?
metal knob
9. A person walks across a carpet, touches a
metal doorknob, and receives a shock. If the
same person were carrying a metal rod, she
would not experience a shock when
touching the doorknob. Why?
10. Suppose a five-year-old child asks you to
explain why there is lightning. Write a
simple explanation that you could share
with the child. You may wish to include a
diagram.
Reflection
11. What are two things about static electricity
that you know now but you did not know
before you started this chapter?
Question 7
For more questions, go to ScienceSource.
Static charges collect on surfaces and remain there until given a path to escape.
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Electrostatics in Our Lives
Here is a summary of what you
will learn in this section:
• Lightning rods are used to
prevent damage to buildings.
• Grounding static charges
can help prevent sparks near
flammable fuels.
• Paint sprayers work better if
the object and the paint have
different charges.
• Photocopiers use electrostatic
principles in their operation.
• Grounding wires prevent
damage to electrical
equipment.
• Electrostatic precipitators work
by creating charged waste
particles and using
electrostatic attraction to
remove the particles.
Figure 10.26 Lightning can strike tall buildings repeatedly during a storm. The CN Tower
(extreme right of photograph) is struck by lightning more than 70 times a year.
Lightning Storm Awareness
On a hot and humid summer night, lightning strikes a building in
Toronto (Figure 10.26). Along with the lightning, there would
have been loud claps of thunder. You may have noticed that as a
storm moves closer, the time between lightning and thunder
decreases. This occurs because lightning travels very fast, at the
speed of light. Thunder travels much more slowly, at the speed of
sound. If you see lightning and hear thunder at the same time, the
storm is right above you.
Summer storms are common in Ontario and across Canada,
but many people do not know what to do in these extreme
weather conditions. Lightning storm safety begins by watching
for towering cloud formations that signal developing storms.
Lightning can strike up to 15 km from where it is raining. As a
guideline, if you can hear thunder, you are in striking distance
and should look for shelter.
Safe shelter includes a large building because it will be
properly grounded if there is a strike. Cars, school buses, and
other vehicles are also safe places, provided that the windows
are rolled up and you do not touch metal parts of the vehicle.
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If no safe shelters are available, you should avoid the highest
point of land because lightning tends to hit these areas. Remain
in a safe place for about 30 minutes after the last thunderclap.
A dangerous place to take shelter during a lightning storm is
under a tree, as the tree may be the highest point in the area. This
makes it more likely to be struck by lightning. Also stay away
from objects that conduct electricity, such as bicycles,
lawnmowers, and golf clubs. Summertime presents a higher risk
of being struck by lightning both because there are more lightning
storms and because more people are outdoors participating in
activities such as baseball, swimming, fishing, and boating.
Lightning strikes cause about six deaths per year in Canada
and result in injuries to about 60 people. All of these could be
prevented if everyone follows the few careful steps just described
as the storm approaches.
D8
STSE Quick Lab
Lightning: Facts and Fiction
Purpose
Questions
To separate lightning facts from lightning fiction
Procedure
1. As a class, read the following true account of one
man’s close encounter with a lightning strike.
Then, discuss the questions that follow.
A man was digging post holes in a large open
field. One of the tools he was using was a 2 m
steel bar, which he used to pry rocks from the
ground. He was working in stormy weather
and wanted to finish a bit more work before
taking cover.
Suddenly, he could feel the hairs on his
arms and legs begin to stand up. He threw the
steel bar as hard as he could and dove for the
ground. Then, he heard a deafening blast of
sound. The lightning strike missed him, and he
ran for cover.
Later, after the storm, he went back to the
site. The ground around the bar was
blackened, and one end of the bar appeared
to have melted.
2. What was his hair standing up an indication of?
3. (a) Holding a steel bar when the lightning struck
would almost certainly be lethal. Why?
(b) Would it make any difference if the steel bar
being held had one end in the ground when
lightning struck? Explain why or why not.
4. Describe the path the lightning may have taken
to result in blackened ground and a melted end
of the steel bar.
5. What could the man have done differently in
order to be safer during the storm?
6. Describe how to keep safe if you find yourself
outside during a thunderstorm.
7. If you find yourself out in the open during a
thunderstorm, you should crouch, keep your feet
close together, and stay on your toes.
(a) Why should you crouch on your toes?
(b) Why should you keep your feet close together?
Static charges collect on surfaces and remain there until given a path to escape.
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Lightning Rods
Figure 10.27 A tree burned by
lightning
When lightning strikes a tree, the sap inside the tree conducts
the electricity down to the ground. In the process, the tree heats
up and expands very rapidly, resulting in an explosion and fire
(Figure 10.27).
If the tree had been wet on the outside and dry on the inside,
the electricity might have followed a different path to the ground
and left the tree unharmed. Or if there had been a conductor, such
as a metal rod, that was slightly taller than the tree and that was
connected to the ground, the lightning strike could have followed
the conductor safely to the ground and left the tree unharmed.
A lightning rod is a metal pole with a wire attached to it that
runs down to the ground. The main purpose of a lightning rod is
to provide a point removed from the main structure of a building
where a stream of electrically charged particles is more likely to
form. The stream of electrically charged particles is highly
conductive, so if lightning strikes in the area around the building,
it is much more likely to strike the lightning rod (Figure 10.28).
This decreases the total amount of electric charge in the building,
which makes it less likely to be struck by lightning. If lightning
hits the lightning rod, the flow of electrically charged particles is
directed harmlessly down to the ground so the building is not
damaged, as shown in Figure 10.29.
lightning
rod
Figure 10.28 The point on top of this
weather vane is a lightning rod.
Figure 10.29 The lightning rod
redirects the electrical strike away
from the barn and harmlessly into the
ground.
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insulated
grounding
wire
ground rod
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Grounding Static Charges on Vehicles
During Reading
Friction occurs when two surfaces rub against each other. The
surfaces may be solids, such as silk or glass, or they may be fluids,
such as air or water. Automobiles and airplanes build up charge
through friction between the vehicle’s outer surface and the air. A
simple way to prevent static build-up on a car is to use a ground
strap (Figure 10.30). However, dragging a strap along the ground
would not be a practical solution for airplanes.
Airplanes have needle-like projections located in various
places on the wings and plane body, as shown in Figure 10.31.
The force of repulsion between charges becomes so strong around
a point that charges will disperse into the air from the point.
Determining the Key Idea
Figure 10.30 Some drivers use a
grounding strap to prevent static charges
from building up on their cars.
Good readers synthesize details
from a text to determine the key
idea. To do this, you make
connections among the important
ideas in the text, asking yourself
the question “How does this
information connect to that
information?” As you read pages
418 to 420, ask yourself how the
information on one page
connects to the information on
another page. What is the single
key idea presented on these
pages?
Figure 10.31 These needle-like rods on the
wing of an airplane disperse static charges
into the air.
Static Charges and Flammable Materials
Static charge build-up is particularly dangerous when
using flammable materials (Figure 10.32). When
airplanes are fuelled, the very explosive fuel moving
through the nozzle creates a build-up of static charges.
If the nozzle comes too close to the plane’s body, a
spark could ignite the fuel. In order to prevent this
from occurring, the nozzle and fuel truck are
connected to the ground. Sparks are also dangerous
near the gas pumps at service stations. It is a good idea
to ground yourself at a service station by touching a
metal door handle before you slide across the seat to
exit a vehicle.
Figure 10.32 The nozzle and fuel truck must be grounded
before refuelling an airplane begins.
Static charges collect on surfaces and remain there until given a path to escape.
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Reducing Static Charges in the Home
Figure 10.33 You can reduce the
build-up of static charges by drying
only the same types of materials at
one time.
You can use your knowledge of static charges to help you
understand how to reduce charges. For example, static charges
are built up when different types of insulators, such as nylon
and polyester, rub together. This is why clothes made of different
materials often stick together when they come out of a clothes
dryer (Figure 10.33).
More charges build up in dry air, such as during winter,
because dry air acts as an insulator. Moist air is a fair conductor,
so fewer charges build up on humid days. If you remove clothes
from the dryer before they are completely dry, there will be fewer
charges on them.
Sometimes, people add an antistatic dryer sheet to a clothes
dryer. The dryer sheet adds a thin layer of waxy chemicals to the
surface of clothes so there is less friction between the surfaces
and therefore fewer unlike charges to attract each other.
Sparks caused by static charges can damage sensitive
electronic equipment. People who work with this type of
equipment take special care to reduce the risk of sparks. For
example, carpets can cause static build-up.
Ways to reduce the risk of static sparks from
carpets include:
• using an antistatic mat for your feet
• increasing the moisture in the air by using a
humidifier
• spraying the carpet with antistatic spray
• wearing an antistatic wrist strap
(Figure 10.34)
• removing the carpet from the computer room
Figure 10.34 This computer technician wears an antistatic wrist strap to
reduce the build-up of charges.
Learning Checkpoint
1. What is the function of a lightning rod?
2. How is charge build-up reduced on airplanes?
3. Why is a ground strap a necessary safety feature when transferring fuel?
4. What are three different methods for reducing charge build-up in clothes
dryers?
5. What are four different methods for reducing charge build-up in a
computer room with a carpet?
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Making Use of Static Charges
Static electricity can be a nuisance when it causes flyaway hair or
sparks in your living room. It can be extremely dangerous when it
occurs near flammable materials or electronic equipment.
However, static electricity can also be useful. Our ability to
control and direct static electricity has allowed us to design
technological devices that make use of it to improve our lives.
Spray Painting
If you have ever tried spray painting, you may have found it to be a
challenging job. The paint comes out in a mist, and you lose a lot
of paint because it doesn’t all land on the object you’re trying to
paint. The paint comes out of the spray gun at a high speed, so the
paint particles bounce off the object being painted, wasting paint.
Electrostatics can help! Figure 10.35 shows a worker making
use of electrostatics to paint a car. The paint coming out of the
nozzle gains a negative charge through friction. The surface of the
car has been given a positive charge. Unlike charges attract, so the
paint is attracted to the surface of the car. There is less waste due
to bounce and overspray, and the finish is smooth and uniform.
Figure 10.35 Industrial sprayers such as those used to paint cars and boats take advantage of
the laws of static charges.
Static charges collect on surfaces and remain there until given a path to escape.
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Take It Further
Laser printers make use of
electrostatics in the printing
process. Find out how a laser
printer works. Start your research
at ScienceSource.
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Photocopying
The word “photocopy” means to copy using light. Figure 10.36
shows the typical steps involved in photocopying, including the
role of electrostatics.
Step 1
A positive charge is created on the drum. The
drum is an insulator, but it becomes a conductor
when exposed to light. For this reason, it is called
a photoconductor.
⫹ ⫹
⫹ ⫹⫹ ⫹ ⫹⫹
⫹
⫹
⫹
⫹
⫹ ⫹⫹ ⫹ ⫹⫹ ⫹ ⫹⫹
⫹
⫹
⫹
⫹
⫹ ⫹
⫹
⫹ ⫹
Suggested Activity •
D10 Quick Lab on page 424
Step 3
Plastic particles and toner (ink) are sprayed onto
the drum. As the particles come out of the
sprayer, they get charged negatively. The
negatively charged toner sticks to the positively
charged areas on the drum, creating a copy of
the original paper.
⫺
⫹
Step 2
The image on the paper to be photocopied is
projected onto the drum. Where the light hits the
drum, the area becomes conductive, loses its
charge, and becomes neutral. The dark areas
remain positively charged.
⫺
⫺
⫺
⫹
⫹
⫹
⫺
⫹
⫺
⫹
Step 4
A sheet of paper is pressed against the drum and
heated. Heat and pressure cause the toner to fuse
to the paper. In some photocopiers, the paper is
also charged to help the toner stick to it.
page to
be copied
light
source
lens
⫹⫹
⫹⫹⫹ ⫹ ⫹⫹ ⫹
⫹ ⫹ ⫹ ⫹⫹ ⫹
⫹⫹ ⫹⫹ ⫹⫹⫹
⫹
Figure 10.36 A model of a photocopying process
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Step 5
The paper is still charged and may be warm when
it comes out of the photocopier.
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Environmental Applications
An electrostatic precipitator makes use of the laws of static
charges to clean air (Figure 10.37). The gas discharged from a
factory can contain tiny particles of pollutants, called particulate
matter. One way to clean the gas before it is released is to send it
through pipes that charge the particulate matter negatively. The
gas then moves through an area that has positively charged plates.
The positive plates attract the negative particles and remove them
from the gas. These collector plates are cleaned periodically to
keep the system running efficiently. Industrial plants that
produce cement, steel, lumber, and petrochemicals use similar
techniques to remove dust from the air.
We also use electrostatics in processes that purify and sort
materials, such as ore separation in mining, plastics and paper
recycling, and the settlement of fine particles suspended in water.
Suggested Activity •
D11 Quick Lab on page 425
clean gas out
Electrostatic
Precipitator
conductors
(metal plates)
polluted gas in
grounding wire
solid waste collection
D9
Figure 10.37 An electrostatic precipitator uses static
electricity to remove particulates from gases in buildings or
industrial sites.
STSE Science, Technology, Society, and the Environment
Advertisements for Static Control Products
If you have a problem with flyaway hair, clothes
sticking together in the dryer, or dust that will not
stick to a mop, chances are there is a consumer
product that has been designed to help you.
Discuss the following questions with your group
and record your answers.
1. Give examples of products that help consumers
with static control.
2. Are these products essential for everyday living?
Why or why not?
3. (a) What do advertisers say about static in their
messages to try to convince you to buy their
products? Is this information accurate?
(b) Do you think they are successful in
convincing people? Explain your answer.
Static charges collect on surfaces and remain there until given a path to escape.
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D10 Quick Lab
Make Your Own Photocopier
Imagine painting your name on a piece of paper
using a paint that attracts electrons. Suppose you
then rubbed the paper with fur, causing your painted
name to gain a negative charge. You could sprinkle
cocoa or flour on the paper and the neutral cocoa or
flour would be attracted to the charged paint. The
cocoa or flour would stick to your name, spelling it
out in black or white. This is basically how a
photocopier works. In this activity, you will investigate
a variation of this technique.
3. Add cocoa or flour to the dish. Jiggle the dish in
order to spread the cocoa or flour evenly.
4. Using a minimum of tape, attach the edge of the
circle to the outside of the lid.
5. Using the wool cloth, gently rub the lid area
showing through the paper for about a minute,
as shown in Figure 10.38.
Purpose
To investigate the principles of photocopying
Materials & Equipment
• paper and scissors
• clear adhesive tape
• plastic petri dish and
lid
• cocoa or flour
• wool cloth
CAUTION: Never eat anything in science class.
Figure 10.38 Rub the lid gently.
6. Carefully remove the stencil. Put the lid on the
dish.
7. Turn the dish upside down while holding the lid.
Then, turn it right side up.
8. Remove the lid. Record your observations.
Procedure
1. Cut a paper circle the size of the petri dish.
2. Turn the paper into a stencil by cutting out a
simple symbol such as a diamond or your initial.
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Questions
9. What did you observe in step 8?
10. How would you explain your observations?
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D11 Quick Lab
Make Your Own Precipitator
An electrostatic precipitator uses static charges to
separate particles in order to purify and sort materials.
Purpose
To study how an electrostatic precipitator works
Materials & Equipment
• paper towels
Figure 10.39 Pull the paper towel across the table slowly.
• ground pepper
• flour
• salt
4. Clean the balloons and recharge them. Repeat
step 3 with the remaining particles on the towel.
• lint
• 3 balloons
5. Clean up your work area. Wash your hands
thoroughly.
CAUTION: Never eat anything in science class.
Questions
Procedure
6. (a) Which particles were the easiest to pick up?
1. Lay a long piece of paper towel on a table.
Sprinkle pepper, flour, salt, and bits of lint on the
paper towel.
2. Inflate and tie off three balloons. Charge the
balloons by rubbing them against your hair or a
sweater. Hold the balloons above the table but
not directly above or touching the paper towel.
3. Have a partner pull the paper towel across the
table slowly under the balloons (Figure 10.39).
Observe which materials are taken up and how
much of the material is left.
(b) Which particles were difficult to pick up?
Explain why.
7. What happened to the ability of the balloons to
pick up particles as time went on?
8. Why do you think this method is used to remove
particulate matter from the air?
9. What factors would affect the efficiency of a
precipitator?
Static charges collect on surfaces and remain there until given a path to escape.
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10.3 CHECK and REFLECT
Key Concept Review
1. Why is it not a good idea to take shelter
under a tree in a thunderstorm?
2. (a) What are the three parts of a lightning
protection system for a building?
(b) What is the function of each part?
3. What causes the static build-up on moving
vehicles such as cars and airplanes?
4. Large trucks that carry flammable liquids
often have a metal wire or chain that drags
on the ground. Why?
5. Sometimes, finished photocopied paper will
stick to you. Explain why.
6. Name four applications that use
electrostatic principles.
Connect Your Understanding
7. Why does Earth not become charged when
many people in the world ground objects?
8. How can neutral pollutant particles be
made attractive to the charged plate in an
electrostatic precipitator?
9. The technician in this photo is using a tool
that has insulated handles. Why is this
important for working on electronic
equipment?
10. When spray paint is applied to a car, the
paint has a negative charge and the surface
of the car has a positive charge. Some
processes use a negatively charged paint
and a grounded object. Explain why this
also works.
11. Flowing fluids, such as water, oil, and air,
produce static charge. Why is it not as
important to create static charge safety
rules for handling flowing water as for
handling air or oil?
12. Suppose you have a static charge problem at
home. Your clothes stick to your body, there
are socks stuck to your sweater from the
dryer, and you always get a shock from
touching a doorknob after walking across
your carpet. Suggest ways you can reduce
or eliminate these and similar problems.
13. Explain the importance of protecting
computer equipment from static discharge.
14. Explain how eliminating static electricity
would hinder the performance of a spray
painting device.
15. Suppose a building had a lightning rod that
was not connected to a ground rod by a
conducting wire. Would this set up still
provide protection from lightning strikes?
Explain.
Reflection
16. Which device that makes use of static
electricity has the greatest effect on your
life? Why?
For more questions, go to ScienceSource.
Question 9
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S C I E N Ceverywhere
E
Deep Brain
Stimulation
This device is sometimes called a
“pacemaker for the brain.” A pacemaker is
an implanted device that supplies electric
signals to the heart to help it beat regularly.
A brain pacemaker causes deep brain
stimulation. It stimulates the brain by
sending electric impulses to target areas
deep within the brain. These electric
impulses interfere with naturally occurring
electric impulses in the brain that cause
uncontrolled shaking, called tremors, in a
patient. Tremors are a symptom of several
conditions, including Parkinson’s disease.
Tremors can prevent people from walking,
feeding themselves, or even just being able
to sit still.
Before receiving the deep brain-stimulating
device, this patient was unable to control his
arms and was unable to speak clearly. With his
new implants sending electric signals to his brain,
he is able to use his steady hand to enjoy a hot cup of
coffee without worrying about spilling it and burning himself.
This X-ray shows how deeply the two
electrodes are placed inside the brain. The
electric signals are generated by a small
device implanted in the patient’s chest,
near the shoulder. The electric circuits are
programmed using a computer that
contacts the device using radio signals. This
means the electric impulses can be
adjusted with the device implanted in the
patient’s body. Using special magnets,
patients or their doctor can even turn the
deep brain stimulator on or off.
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10 CHAPTER REVIEW
ACHIEVEMENT CHART CATEGORIES
t Thinking and investigaion
k Knowledge and understanding
c Communication
a Application
5. (a) Describe how to leave an object
positively charged using the induction
method. k
Key Concept Review
1. (a) What are the possible interactions
between two charged objects? k
(b) How do a charged object and a neutral
object interact? k
(b) Describe how to leave an object negatively
charged using the induction method. k
6. How would you ground an electroscope?
7. (a) Define electrical discharge.
(b) What is a real-life example of an
electrical discharge? k
2. Explain the role of friction in creating a
charged object. k
3. (a) Two neutral objects, A and B, were
rubbed together, resulting in object A
being charged positively. What is now
the charge on B? k
(b) How do you know?
k
(c) Which object, A or B, is likely higher on
the triboelectric series? k
(d) How do you know?
k
4. For the following three electroscopes,
explain which way the leaves will move
when a charged rod is brought near.
Explain your reasoning. t
+
+
–
+
+
–
(a)
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–
9. Describe a device that protects other devices
by controlling static electric charges. Include
a labelled diagram as part of your answer. c
Connect Your Understanding
10. Explain why a positively charged balloon
will stick to a wall just as easily as a
negatively charged balloon. t
11. Would the humidity (moisture content) of
the air make a difference in the
photocopying process? Explain. t
–
+
(b)
UNIT D
8. Describe a device that uses static electric
charges. Include a labelled diagram as part
of your answer. c
–
+
+
–
The Characteristics of Electricity
k
+
–
–
–
–
+
(c)
–
–
Question 4
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12. Suppose you had a plastic lightning rod that
was the same size and design as a metal
lightning rod. Would the plastic lightning
rod work better than, the same as, or not as
well as a metal lightning rod? Explain your
answer. t
13. Would a negatively charged balloon stick to
a metal wall as easily as to a wooden wall?
Explain why it would or would not. t
14. You have an unknown material that
becomes charged when you rub it with silk.
You also have a negative ebonite rod and a
positive glass rod. How can you determine
the charge of the unknown object? t
21. What materials could be woven into a
polyester carpet to prevent a static charge
from building up on a person walking
across the carpet? Explain the reasons for
your choice. a
Reflection
22. What information from this chapter
surprised you or was not what you
expected? Explain why. c
23. (a) How would you rate your participation
in the labs you did in this chapter? c
(b) How could you improve your
participation? c
15. If lightning hits a car, the effect is minimal.
Explain why. a
16. Two identical objects are both charged
positively, but one object has about twice as
much positive charge as the other object.
What would happen to the charges when
the two objects are brought together?
Explain your answer. t
17. (a) How would using a humidifier in a
home affect static charge build-up?
a
(b) Would you need to use a humidifier
more in the summer or the winter?
Explain. a
18. Explain two different actions that could
cause static charges to build up on a
computer. a
19. If you wrap plastic wrap on a glass bowl,
the plastic wrap will cling to the bowl. Use
your understanding of static charge to
explain why. a
20. You run a brush through your hair and
wonder if it has become statically charged.
Design a test that allows you to determine if
the brush has a charge. t
After Reading
Reflect and Evaluate
Revisit the key learning goals that you set in the
Before Reading activity at the start of this chapter.
How did the During Reading strategies help you to
accomplish your goals? Write a paragraph that
summarizes how the reading strategies assisted
your learning. Compare your paragraph with a
partner’s. Add any new insights you gained from
reading your partner’s reflection.
Unit Task Link
Storing large amounts of electricity is very difficult.
This means that electricity is usually generated as
it is being used. Generating facilities increase and
decrease the amount of electricity they produce
depending on how much electricity the
community is using at any given time. Explain how
an electrical grid connecting many different
electrical generating sources and several
communities provides a dependable source of
electricity. Brainstorm a list of different ways of
generating electricity. Sort them from most
important to least important. Share your ideas with
your class.
Static charges collect on surfaces and remain there until given a path to escape.
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11
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Current electricity is the continuous flow
of electrons in a closed circuit.
The Characteristics of Electricity
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Skills You Will Use
Millions of light bulbs light up the Toronto skyline.
Each light bulb is lit because of the movement of
electrons through the wires that connect the bulbs.
In this chapter, you will:
• design, draw, and construct series circuits and parallel circuits
• analyze the effects of adding an identical load in series and
in parallel
• investigate the relationships between potential difference,
current, and resistance
• solve simple problems using the formula V = IR
Concepts You Will Learn
In this chapter, you will:
• describe the relationship between potential difference,
current, and resistance
• explain what different meters measure and how they
measure electrical quantities
• identify and explain the parts of a simple circuit
• explain the characteristics of electric current, potential
difference, and resistance and how they differ in series and
parallel circuits
• explain how different factors change the resistance of an
electric circuit
Why It Is Important
Every electrical appliance or device that you use includes one
or more electric circuits. Understanding how electrical energy
is produced, transferred, and converted into other forms of
energy will help you handle electrical devices safely.
Before Reading
Learning Vocabulary in Context
This chapter contains many new terms related to
electricity. Skim and scan section 11.1 for the ways that
vocabulary is supported. Where can you find definitions?
How are unfamiliar terms highlighted in the text? What
special features explain terms or words? Begin a
personal list of unfamiliar terms, adding definitions as
you find them in the chapter.
Key Terms
• ammeter • amperes • battery • electric current • fuse
• load • ohms • potential difference • resistance
• switch • volt • voltmeter
Current electricity is the continuous flow of electrons in a closed circuit.
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11.1
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Current, Potential Difference, and Resistance
Here is a summary of what you
will learn in this section:
• An electrochemical cell
generates a potential difference
by creating an imbalance of
charges between its terminals.
• Potential difference is the
difference in electric charge
between two points that will
cause current to flow in a
closed circuit.
• Current is the rate of
movement of electrons through
a conductor.
• An electric circuit is a path
along which electrons flow.
• Resistance is the ability of a
material to resist the flow of
electrons.
• Resistance in a wire depends
on wire length, material,
temperature, and crosssectional area.
Figure 11.1 The elephantnose fish has tiny electric sensors in its nose that help it find
food.
Electric Fish, Eels, and Rays
Figure 11.2 The electric eel uses
electricity to defend itself and to stun
its prey.
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UNIT D
You probably know that when it comes to electrical safety, it is
very important to keep electrical devices away from water. For
some animals, this safety concern about electricity is not a
problem. In fact, they survive because they can use electricity in
the water.
The elephantnose fish from central Africa has an extended
nose that contains about 500 electric sensors (Figure 11.1) These
sensors are used to help this tiny fish find food. The elephantnose
fish hides for protection during the day and comes out to feed at
night. The electric sensors help it find smaller living things
crawling along the bottom of the river or swimming in the water.
Research has shown that these electric sensors are so sensitive
that they can detect chemical pollutants. Further research will
determine if this type of sensor can be used to monitor the levels
of pollutants in rivers.
The Characteristics of Electricity
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The electric eel in Figure 11.2 lives in the murky waterways of
the Amazon and Orinoco river basins of South America. It’s
really a fish and not an eel, but it really is electric — and
dangerous. The eel’s electricity comes from a special organ in its
long tail that contains thousands of muscle cells that work like
tiny batteries. Each cell can produce only a small amount of
electricity, but by working together all the cells can produce
controlled bursts of electricity equal to five times the energy of a
standard wall socket. These electrical bursts are used to stun prey
when the electric eel is hunting for food. Some electric eels also
generate an electric signal to attract a mate.
The Pacific electric ray, found along the west coast of North
America, has an electric organ located in its head (Figure 11.3).
This organ can generate enough electricity to knock down a
human. Other types of electric rays use these electric shocks for
defense when they are attacked. Rays belong to a category of
animals called Torpedo. The name for this category comes from
the Latin word torpidus, which means numbness. This term
describes what happens to a person who steps on an electric ray.
Figure 11.3 A Pacific electric ray
can send out a powerful electric
shock.
D12 Quick Lab
Light the Lights
In this activity, you will use a combination of wires,
light bulbs, and an electrochemical cell to investigate
how a steady, controlled flow of electrons can cause
the bulbs to light up.
Procedure
1. Use wire and the dry cell to make one bulb light
up. Record your arrangement.
2. Use wire and the dry cell to make two bulbs light
up. Record your arrangement.
Purpose
To discover how to make flashlight bulbs light up
using a standard battery
3. If time allows, try other arrangements for step 1
and step 2.
Questions
4. Explain how to use wire and a dry cell to make
one bulb light up. Include a labelled sketch in
your answer.
Materials & Equipment
• 1 D dry cell
• 5 insulated copper wires with both ends bare
5. Explain how to use wire and a dry cell to make
two bulbs light up. Include a labelled sketch in
your answer.
• two 2.0 V-flashlight bulbs
CAUTION: Disconnect the wires if they get hot. Do not
use dry cells if they show any sign of corrosion.
Current electricity is the continuous flow of electrons in a closed circuit.
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During Reading
Illustrations
Support Understanding of
Vocabulary
As you read the text, be aware
of how the photos, diagrams, or
other illustrations support your
understanding of unfamiliar
vocabulary. What term or
concept is illustrated by the
photo or diagram? How does the
illustration make the concept
easier to understand? If you get
stuck on unfamiliar terminology,
check the illustrations as one
way to improve your
understanding.
W O R D S M AT T E R
The word “circuit” comes from a
Latin word meaning to go around.
The word “circuit” can also be used
to describe a complete journey of
people or objects, such as the circuit
of Earth around the Sun.
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Current Electricity
The electricity of the electric eel and the electric ray is similar to
the static charges you have felt from a sweater or the huge static
charges of lightning. Unfortunately, static charges are not useful
for operating electrical devices. They build up and discharge, but
they do not flow continuously.
To operate electrical devices, you need a steady flow of
electrons. Unlike static electricity, a flow of electrons moves
continuously as long as two conditions are met. First, the flow of
electrons requires an energy source. Second, the electrons will not
flow unless they have a complete path to flow through. This path
is called an electrical c i rc u i t. The continuous flow of electrons in
a circuit is called c u r re n t e l e c t r i c i t y.
Electric Circuits
A circuit includes an energy source, a conductor, and a load. An
electrical l o a d is a device that converts electrical energy to
another form of energy. For example, in Figure 11.4, the light bulb
is the load. It converts electrical energy to light and heat.
Many electric circuits also include a switch. A s w i t c h is a
device that turns the circuit on or off by closing or opening the
circuit. When the switch is closed, the circuit is complete and
electrons can flow. An open switch means there is a break in the
path, so the electrons cannot flow through the circuit. The circuit
is turned off when the switch is open.
energy source
+
electrical load
conducting wires
switch
Figure 11.4 An electric circuit
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Electrochemical Cells
One simple and convenient energy source is a battery. A b a t t e r y
is a combination of electrochemical cells. Each e l e c t ro c h e m i c a l
c e l l is a package of chemicals that converts chemical energy into
electrical energy that is stored in charged particles. A simple
electrochemical cell includes an electrolyte and two electrodes.
• An electrolyte is a liquid or paste that conducts electricity
because it contains chemicals that form ions. An ion is an
atom or a group of atoms that has become electrically
charged by losing or gaining electrons. Citric acid is an
example of an electrolyte.
• Electrodes are metal strips that react with the electrolyte.
Two different electrodes, such as zinc and copper, are used
in a battery.
As a result of the reaction between the electrolyte and electrodes,
electrons collect on one of the electrodes, making it negatively
charged. The other electrode has lost electrons, so it is positively
charged (Figure 11.5).
copper electrode (+)
zinc electrode (–)
F
D
B
Figure 11.5 The citric acid in the grapefruit is the electrolyte. Electrons collect on the zinc
electrode, leaving positive charges on the copper electrode. The meter measures the flow
of electrons.
C
A
E
Wet Cells and Dry Cells
An electrochemical cell that has a liquid electrolyte is called a wet
cell. Wet cells are often used as an energy source for cars and
other motorized vehicles. An electrochemical cell that uses a paste
instead of a liquid electrolyte is called a dry cell (Figure 11.6).
You use dry cells in flashlights, hand-held video game devices,
cameras, and watches. Each electrode in a dry cell or battery can
also be called a terminal. Terminals are the end points in a cell or
battery where we make a connection.
A – zinc powder and electrolyte,
where electrons are released
B – electron collecting rod
C – separating fabric
D – manganese dioxide and carbon,
where electrons are absorbed
E – negative terminal, where electrons leave
F – positive terminal, where electrons return
Figure 11.6 An alkaline dry cell
Current electricity is the continuous flow of electrons in a closed circuit.
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Recycling and Recharging Dry Cells
Eventually, the chemicals in a dry cell are used up and can no
longer separate charges. When you are finished using a dry cell,
you should recycle it rather than discard it (Figure 11.7). Dry cells
can contain toxic materials, such as the heavy
metals nickel, cadmium, and lead. Household
dry cells and batteries are responsible for over
50 percent of all the heavy metals found in
landfills.
Some dry cells are rechargeable cells.
Chemical reactions in a rechargeable cell can be
reversed by using an external energy source to
run electricity back through the cell. The
reversed flow of electrons restores the reactants
that are used up when the cell produces
electricity. Since rechargeable dry cells can be
reused many times, they have less impact on
the environment than non-rechargeable dry
Figure 11.7 During recycling, the chemicals in a dry cell are
separated and can be reused.
cells.
Fuel Cells
A fuel cell is an electrochemical cell that generates electricity
directly from a chemical reaction with a fuel, such as hydrogen
(Figure 11.8). The cell is not used up like an ordinary cell would
be because as the electricity is produced, more fuel is added.
Much of the energy produced by fuel cells is wasted as heat, but
their design continues to be refined. Fuel cells are used in electric
vehicles and may one day be used in smaller devices such as
laptop computers.
Learning Checkpoint
1. How is current electricity different from static electricity?
2. What is an electric circuit?
Figure 11.8 A fuel cell converts
chemical energy into electrical
energy. This fuel cell is slightly
smaller than this textbook.
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3. List three components of an electric circuit.
4. What is the difference between an electrolyte and an electrode?
5. Why should dry cells be recycled rather than thrown in the trash?
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Potential Difference
Each electron has electric potential energy. Potential energy is
the energy stored in an object. Picture an apple hanging from a
low branch on an apple tree (Figure 11.9). The apple has potential
energy because of its position above the ground. If the apple falls
down, it will convert its stored energy, or potential energy, into
motion. Suppose an apple were on a higher branch. It would have
even more potential energy to convert.
W O R D S M AT T E R
The electrochemical cell was first
presented to the Royal Society of
London in 1800 by the Italian
physicist Alessandro Volta. The words
“voltage and “volt” are named in his
honour.
Figure 11.9 The greater the height of an apple above the ground, the
greater its potential energy.
A battery has chemical potential energy in the electrolyte in
its electrochemical cells. The chemicals in the electrolyte react
with the electrodes. This causes a difference in the amount of
electrons between the two terminals. One terminal in a battery
has mainly negative charges (electrons). The other terminal has
mainly positive charges (Figure 11.10). The negative charges are
electrons, which can move. They are attracted to the positive
charges at the positive terminal. If a conductor, such as a copper
wire, is connected to both terminals, then the electrons flow from
the negative terminal to the positive terminal.
The difference in electric potential energy between two points
in a circuit is called the potential difference or voltage (V).
This difference causes current to flow in a closed circuit. The
higher the potential difference in a circuit, the greater the
potential energy of each electron.
–– +
– +
–––
– + ++
++
Figure 11.10 An electrochemical
cell or battery gives electrons
electric potential energy.
Current electricity is the continuous flow of electrons in a closed circuit.
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Measuring Potential Difference
The potential difference between two locations in a circuit is
measured with a voltmeter. For example, you could place the
connecting wires of the voltmeter across the positive and negative
terminals of a battery like the rectangular yellow box shown in
Figure 11.11. The voltmeter would then display the potential
difference of the battery. The SI unit for measuring potential
difference is the volt (V).
How Electrons Transfer Energy in a Circuit
Figure 11.11 The orange device is a
voltmeter. It is showing a reading of
1.50 V. The yellow device is a
battery.
When you turn on the light switch on a wall, you close the circuit
and immediately the light comes on. How do the electrons get
from the switch to the light bulb so fast? It may surprise you to
learn that electrons do not travel from the switch to the bulb. You
can picture electrons in a wire as being like water in a hose. If a
hose connected to a tap already has water in it and you turn the
tap on, water comes out of the end of the hose immediately.
Electrons in a wire work in a similar way. When an energy
source is connected to a circuit, electrons in the conductor “push”
or repel other electrons nearby. As soon as one electron starts to
move at one end of the wire, it pushes the next one, which pushes
the next one and so on. By pushing the first electron, you make
the last electron move (Figure 11.12). That is why when you flip
the switch, the light goes on instantly even though the electrons
themselves have not moved from the switch to the light bulb.
Figure 11.12 Electrons in a wire are like marbles in a tube. If you push a marble at one
end of the tube, the energy is transmitted through all the marbles. When electrons in a
wire are “pushed” from one end, energy is transmitted all along the electrons in the wire.
Learning Checkpoint
1. What is another name for stored energy?
2. How is an apple falling from a tree like the potential difference in a battery?
3. What does potential difference measure?
4. What is another name for potential difference?
5. When you walk into a dark room and turn the light on, do the electrons
travel all the way from the switch to the light? Explain your answer.
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Current
Electric current is a measure of the amount of electric charge
that passes by a point in an electrical circuit each second. Think
of the continuous flow of electric current as being like water
flowing in a stream. The water keeps on flowing unless its source
dries up. As long as the battery continues to separate charges on
its terminals, the electrons continue to flow. Because the current
flows in only one direction it is called direct current (DC).
The flow of current from batteries is DC, but the current that
flows through cords plugged into the wall sockets in your home is
called alternating current. Alternating current (AC) flows back
and forth at regular intervals called cycles. This is the current that
comes from generators and is carried by the big power lines to
your home.
Measuring Current
W O R D S M AT T E R
Current in a circuit is measured using an ammeter, as shown in
Figure 11.13. The unit of electric current is the ampere (A). An
ampere is a measure of the amount of charge moving past a point
in the circuit every second.
“Ampere” and “ammeter” are named
in honour of André-Marie Ampère
(1775–1836), a French physicist who
studied electricity and magnetism.
Figure 11.13 These ammeters show a reading of 0.50 A. The meter on the right has
amperes on the scale below the black curved line.
Current Electricity and Static Electricity
Current electricity is different from static electricity because
current electricity is the flow of electrons in a circuit through a
conductor. Static electricity is the electric charge that builds up on
the surface of an object. Static electricity discharges when it is
given a path, but it does not continue to flow.
Current electricity is the continuous flow of electrons in a closed circuit.
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Electron Flow and Conventional Current
Throughout this unit, we refer to current in terms of electrons
flowing from a negative terminal to a positive terminal in a
battery. However, when scientists studied electricity several
hundred years ago, they did not yet know about electrons. They
inferred that when electric current flowed from one object to
another, it did so because one object had a greater amount of
electricity, so the electricity flowed from the higher or more
positive source to the lesser or more negative source. The
mathematical equations and conventions developed afterward
followed this assumption. This view is called conventional
current, and it is a different way of describing the movement of
electrons in a circuit (Figure 11.14).
(c)
–
(d)
(b)
+
(a)
Figure 11.14 Conventional current describes current as leaving the source from the positive
terminal (a) and entering the meter at its positive terminal (b). Then, the current is described
as passing through the meter and leaving through the negative terminal (c). It then returns to
the negative terminal of the source (d).
When you connect an ammeter or voltmeter to a circuit, you
need to think in terms of conventional current rather than
electron flow (Figure 11.15). There are two terminals on a meter
that you use to connect to a circuit. The negative (–) terminal is
often black, and the positive (+) terminal is often red. Always
connect the positive terminal of the meter to the positive terminal
of the electrical source. Connect the negative terminal of the
meter to the negative terminal of the electrical source.
Figure 11.15 When you connect an electrical meter, follow the rule “positive to positive,
and negative to negative.” The positive red terminal of the meter is connected to the
circuit. The positive red terminal of the battery is also connected to the circuit. The
negative black terminals of the meter and the battery are connected directly.
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Resistance
Resistance is the degree to which a substance opposes the flow of
electric current through it. All substances resist electron flow to
some extent. Conductors, such as metals, allow electrons to flow
freely through them and have low resistance values. Insulators resist
electron flow greatly and have high resistance values. Resistance is
measured in ohms (⍀) using an ohmmeter. An ohmmeter is a
device for measuring resistance. An ohmmeter is usually part of a
multifunctional meter called a multimeter (Figure 11.16).
When a substance resists the flow of electrons, it slows down
the current and converts the electrical energy into other forms of
energy. The more resistance a substance has, the more energy it
gains from the electrons that pass through it. The energy gained
by the substance is radiated to its surroundings as heat and/or
light energy (Figure 11.17).
Figure 11.16 Multimeters can be
used to measure potential
difference, current, or resistance.
W O R D S M AT T E R
Figure 11.17 When electrons pass through a resistor, such as the element on this electric
The symbol for ohm, ⍀, is the Greek
letter omega.
heater, their electrical energy is converted to heat and to light.
Resistance in a Circuit
The more resistance a component has, the smaller its conductivity.
For example, current in a circuit might pass through the filament
in a light bulb (Figure 11.18). The filament is a resistor, which is
any material that can slow current flow. The filament’s high
resistance to the electron’s electrical energy causes it to heat up
and produce light.
filament
Figure 11.18 The filament in a
light bulb is an example of a
resistor.
Current electricity is the continuous flow of electrons in a closed circuit.
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Resistors and Potential Difference
high potential energy
potential energy converted
to another form of energy
Figure 11.19 An electron entering a
resistor is similar to a ball at the
high end of a ramp, where potential
energy is greater.
Figure 11.20 Resistors come in
many shapes and sizes. The type of
material the resistor is made from
affects its resistance.
Resistors can be used to control current or potential difference in
a circuit. When you work with resistors, you should always be
aware that they can heat up and cause burns. Use caution when
handling them.
In a circuit, electrons have a higher potential difference as
they enter a resistor compared to when they leave the resistor
because they use up some energy in passing through the resistor.
You can picture electrons entering a resistor as being at the high
end of a ramp, where they have a lot of potential energy. In this
analogy, electrons leaving the resistor are at the bottom end of the
ramp, where their potential energy has been converted to another
form of energy (Figure 11.19).
Types of Resistors
A wide variety of resistors are made for different applications,
especially in electronics (Figure 11.20). For example, televisions
contain dozens of different resistors.
Resistors can be made with a number of techniques and
materials, but the two most common types are wire-wound and
carbon-composition. A wire-wound resistor has a wire made of
heat-resistant metal wrapped around an insulating core. The
longer and thinner the wire, the higher the resistance.
Wire-wound resistors are available with values from 0.1 ⍀ up to
200 k⍀. The wire for a 200-k⍀ resistor is very thin.
Carbon-composition resistors are made of carbon mixed with
other materials. The carbon mixture is moulded into a cylinder
with a wire at each end. By varying the size and composition of
the cylinder, manufacturers produce resistances from 10 ⍀ to
20 M⍀. Moulded carbon resistors are cheaper to make than wirewound resistors but less precise.
Learning Checkpoint
1. What is electric current?
2. What does “resistance” refer to in terms of electron flow?
3. Copy and complete the following table in your notebook. Some answers are
provided for you.
Quantity
Suggested Activities •
D13 Quick Lab on page 444
D14 Quick Lab on page 445
D15 Design a Lab on page 446
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The Characteristics of Electricity
Abbreviation
Unit
Symbol
Potential difference
ampere
⍀
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Resistance in a Wire
Take It Further
The flow of water in pipes is another useful model of electricity
(Figure 11.21). Not all pipes transport water equally well. The
longer and thinner a pipe is, the more resistance it has to the flow
of water. A pipe with a bigger diameter has less resistance, which
allows a greater flow of water.
Similarly, the amount of resistance in a circuit affects the
electrical current. For any given potential difference, current
decreases if you add resistance. As with water flow, you get the
least resistance with a short, wide path with no obstructions. The
shorter and thicker the wire, the less resistance it creates for
electrons. Other factors affecting the resistance of a wire include
the material it is made from and its temperature, as shown in
Table 11.1.
A number of rechargeable dry
cells are available, such as NiCd,
NiMH, and lithium ion. Research
the different types of rechargeable
dry cells. Compare their
composition, lifetime, cost, and
ability to hold charges. Begin your
research at ScienceSource.
Figure 11.21 Resistance in a pipe reduces the flow of water. The smaller the pipe,
the greater the resistance, so the flow is less. Resistance in a conductor reduces the
flow of electrons.
Table 11.1 Factors Affecting the Resistance of a Wire
Factor
How Factor Affects Resistance
Material
Silver has the least resistance but is very expensive to use
in wires. Most conducting wires are made from copper.
Temperature
As the temperature of the wire increases, its resistance
increases and its conductivity decreases. In other words, a
colder wire is less resistant than a warmer wire.
Length
Longer wires offer more resistance than shorter wires. If
the wire doubles in length, it doubles in resistance.
Cross-sectional area
Wider wires offer less resistance than thinner wires. If the
wire doubles in width, its resistance is half as great.
Conducting wires that carry large currents need large
diameters to lessen their resistance.
Current electricity is the continuous flow of electrons in a closed circuit.
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D13 Quick Lab
Make Your Own Dimmer Switch
Some homes have dimmer switches on their lights.
A dimmer switch allows you to adjust light levels in
a room from nearly dark to very bright by moving a
lever or turning a knob.
Purpose
To use resistance to control the amount of current
flowing through a light bulb
Materials & Equipment
• battery
• connecting wires with alligator clips
• flashlight bulb (2.5 W) and socket
• 40-cm of 32-gauge Nichrome™ wire
• piece of wood with screws (see Figure 11.22)
Procedure
1. Connect the battery to the light bulb, and set up
the Nichrome™ wire on the board as shown in
Figure 11.22. Make sure the Nichrome™ wire is
connected at one end but not the other, leaving
your circuit open. Have your teacher approve
your set-up before you proceed further.
2. Close your circuit by connecting the other end of
the Nichrome™ wire, maximizing the length of
the wire in the circuit. Note the brightness of the
bulb (Figure 11.22(a)).
3. Move the alligator clips on the Nichrome™ wire
closer together (Figure 11.22(b)). Note the
brightness of the bulb.
4. Continue to observe the brightness of the bulb
as you move one of the alligator clips along the
Nichrome™ wire.
Questions
5. (a) How did the brightness of the bulb change as
you moved the alligator clips?
(b) Explain why the brightness changed as the
length of wire changed.
6. How do your observations in this activity help
explain how a dimmer switch works?
(b)
(a)
Figure 11.22 The brightness of the bulb changes, depending on whether the space between the clips on the wire is
(a) larger or (b) smaller.
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D14 Quick Lab
Modelling Potential Difference, Current, and Resistance
A model in science can help you picture a process or
object that may be hidden from view or that may be
too large or too small to view directly. You can also
use a scientific model to help you communicate your
ideas.
Purpose
To model interactions among potential difference,
current, and resistance using water flowing in a hose
6. While the water is running, pinch the end of the
tubing slightly. Observe what happens to the
flow. Empty the bucket (if using) when you have
finished timing.
7. Record the time it takes to fill the beaker or
bucket using the slightly pinched length of
tubing. Empty the container when you have
finished timing.
8. Record the time it takes to fill the beaker or
bucket using an open length of tubing.
Materials & Equipment
• 50-cm or longer length
of rubber tubing
• 1000-mL beaker or
bucket
• water tap and sink or
bucket
• stopwatch
10. Follow your teacher’s instructions for cleaning
up.
Procedure
Questions
1. Create a data table with headings like the ones
shown below. Give your data table a title.
2. Attach one end of the tubing to a tap. Place the
other end of the tubing in a bucket or sink as far
from the tap as the tubing will reach without
bending.
3. Turn on the cold water to a medium flow. Record
the time it takes for water to exit the tubing.
4. Pinch the end of the tubing, and then turn off
the water. Keep the end pinched. Empty the
bucket (if using) when you have finished timing.
5. Turn on the cold water to a midway point, and
release the end of the tubing at the same time.
Record the time it takes for water to exit the
tubing into the sink or bucket.
Time to Exit Empty
Tube (s)
9. Record the time it takes to fill the beaker or
bucket using an open length of tubing and the
water turned on full. Empty the container when
you have finished timing.
Time to Exit
Pinched Tube (s)
11. (a) How did the exit times compare for the tubes
in step 3 and step 5?
(b) How would you explain any difference in
times?
12. What part of this activity modelled electric
current in a circuit?
13. (a) How does the size of the opening in the
tubing affect water flow?
(b) Relate the size of the opening of the tubing to
resistance in wires.
14. (a) How does how far a tap is opened affect
water flow through the tubing?
(b) Relate how far a tap is opened to potential
difference in a circuit.
Time to Fill Beaker
or Bucket with
Pinched Tube (s)
Time to Fill Beaker
or Bucket with
Open Tube (s)
Time to Fill Beaker
or Bucket with
Water on Full (s)
Current electricity is the continuous flow of electrons in a closed circuit.
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SKILLS YOU WILL USE
D15 Design a Lab
Skills Reference 2
Investigating Conductivity
Question
How does the conductivity of different solutions
compare?
Materials & Equipment
• 100-mL graduated
cylinder
• 250-mL beaker
• distilled water
• conductivity tester
• tap water
• vinegar
• copper(II)
sulphate solution
• other solutions
provided by your
teacher
• salt water
Using equipment, materials,
and technology accurately and
safely
Adapting or extending
procedures
4. Place the metal tips of the conductivity tester in
the distilled water (Figure 11.23). Record the
conductivity reading of the distilled water in your
table. If your conductivity tester is a light bulb,
describe the brightness of the bulb.
5. Repeat steps 3 and 4 with 50-mL samples of tap
water, salt water, vinegar, copper(II) sulphate
solution, and any other solutions your teacher
provides for you to use. After each conductivity
measurement, empty the beaker as directed by
your teacher and rinse it with distilled water.
Also, wipe off the tips of the conductivity tester.
Make sure that you insert the tips to the same
depth in each solution.
6. Clean up your work area. Make sure to follow
your teacher’s directions for safe disposal of
materials. Wash your hands thoroughly.
Part 2
7. Plan an investigation to compare the conductivity
of other solutions. Have your teacher approve
your plan, and then conduct your investigation.
Analyzing and Interpreting
Figure 11.23 Conductivity tester
9. Rank the substances in order of high
conductivity to low conductivity.
Procedure
Part 1
10. How did your results compare with your predictions?
1. Read through the procedure. Then, design a
data table to record your predictions and your
conductivity readings of the solutions you will
test. Give your table a title.
2. Predict which solutions will be the best conductors
and which will be the poorest conductors. Record
your predictions and the characteristics on which
you are basing your predictions.
3. Put 50 mL of distilled water into a 250-mL
beaker.
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8. How did you determine whether there were
differences in conductivity between the solutions
you tested?
The Characteristics of Electricity
Skill Practice
11. Make an hypothesis about why there were
differences in conductivity between the
solutions.
Forming Conclusions
12. Write a summary of your results that answers the
question “How does the conductivity of different
solutions compare?”
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11.1 CHECK and REFLECT
13. Make a list of similarities between the flow
of water and an electric circuit.
Key Concept Review
1. (a) Describe the two main components of
an electrochemical cell.
(b) How does a wet cell produce electricity?
2. What direction do electrons flow in a
circuit?
3. (a) What device measures potential
difference?
14. A student is planning to test several different
electrode combinations to see which would
produce the greatest potential difference in a
wet cell. State whether each of her choices
will work. Explain why or why not. Her
choices for electrodes are as follows:
(a) both zinc
(b) zinc and copper
(b) What are the units for measuring
potential difference?
(c) both copper
15. The illustration below shows a design for a
dry cell. How does this design differ from the
dry cell shown in Figure 11.6 on page 435?
4. (a) What device measures current?
(b) What are the units for measuring
current?
5. What is the difference between potential
difference and current?
zinc can
(negative
electrode)
insulated
casing
insulator
positive
terminal
6. What is the difference between DC
electricity and AC electricity?
7. (a) What is the function of an electrical
load in a circuit?
(b) List four examples of electrical loads.
8. What does resistance refer to in a circuit?
9. What is the role of a resistor in a circuit?
10. What are four factors affecting resistance in
a wire?
electrolyte
paste
negative
terminal
carbon
electrode
insulator
Question 15
Reflection
Connect Your Understanding
11. Why must a circuit be closed in order for a
current to flow?
16. What do you now understand about current
electricity that you did not know before
reading this chapter?
12. Use a three-circle Venn diagram to compare
and contrast alternating current, direct
current, and static electricity.
For more questions, go to ScienceSource.
Current electricity is the continuous flow of electrons in a closed circuit.
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Series Circuits and Parallel Circuits
Here is a summary of what you
will learn in this section:
• A circuit diagram represents an
electric circuit.
• An ammeter is hooked up in
series to measure current.
• A voltmeter is hooked up in
parallel to measure voltage.
• In a series circuit, the current
is constant and the voltages
across resistors add up to the
total voltage.
• In a parallel circuit, the
voltages are constant and the
currents on each path add up
to the total current.
Figure 11.24 These toy robot dogs are controlled by electric circuits.
Designing Circuits
Computers and the toy robots in Figure 11.24 have complex
circuits. Other electrical devices such as a flashlight or a hair
dryer have much simpler circuits. The simplest circuit is a loop.
An ordinary flashlight can be designed this way. If you take a
flashlight apart, you will probably find a light bulb, some wire, a
couple of batteries, and a plastic casing to hold and protect the
electrical parts. This design works very well for providing light
when it is dark. It also works well in terms of cost. Flashlights are
easy to build with readily available materials and can be
assembled efficiently.
A simple loop isn’t always the best design when there are a
variety of different components in the circuit. Designers have to
ensure that one component does not depend on another. For
example, it would be very frustrating to the user if the toy robot
stopped working because one of its light bulbs went out. You
would probably be upset if your computer at school stopped
working because an LED indicator burnt out. In these devices,
multiple electrical loops are used so that if one component stops
working, the rest of the device will continue to function.
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Tiny Circuits
Conventional switches and other electrical components are
practical and convenient for homes or simple electrical devices.
But for the miniature circuits in advanced electronic devices such
as computers, transistors must be used instead. A transistor is a
tiny device that acts as a switch or amplifier in a circuit.
Transistors are often referred to as solid-state components
because they are made of solid material with no moving parts.
Most transistors are constructed with three layers of specially
treated silicon. These layers are arranged so that a small potential
difference through the middle layer controls a current between
the outer layers. In this way, transistors can act as switches.
Microcircuits (also called integrated circuits) are made up of
microscopic transistors and other electrical devices. A
microcircuit is exactly what its name suggests: a circuit on an
extremely small scale. Microcircuits regularly contain more than a
million components per square centimetre (Figure 11.25).
Figure 11.25 A microcircuit is
usually called a “chip” or a
“microchip.”
D16 Quick Lab
Keep the Lights On
Current flows when a circuit is complete. If there is a
break in a circuit, due to a burned-out bulb, for
example, the current cannot continue. In this activity,
you will investigate how to keep current flowing
through a circuit even though one bulb may be
burned out or missing.
Purpose
To compare the flow of electrons in two different
circuits
Procedure
1. Circuit A: Using any of the materials, hook up
three bulbs in a row so they all light up. Make a
labelled diagram of your set-up.
2. Circuit B: Hook up all three bulbs so that you can
remove one bulb without disconnecting the wires
and still have the other bulbs stay on. Make a
labelled drawing of your set-up.
Questions
3. (a) What would happen to the other two bulbs if
you removed one bulb in Circuit A?
Materials & Equipment
• 1 D dry cell
• 5 insulated copper wires with both ends bare
• three 2.0-V flashlight bulbs
CAUTION: Open the circuit if the wires get hot.
(b) Why would this happen?
4. Why did the other two bulbs stay lit when you
removed one bulb in Circuit B?
5. Draw a circuit that would allow you to remove two
bulbs and yet have the third bulb stay lit. Have
your teacher approve your drawing. If time allows,
test your ideas by building the circuit.
Current electricity is the continuous flow of electrons in a closed circuit.
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Circuit Diagrams
load
switch
conducting wire
electrical source
Figure 11.26 The four basic parts of
a circuit
Quit
Engineers and designers of electrical circuits use special symbols
that show the components and connections in a circuit. These
symbols make it easier to plan and analyze a circuit before you build
it. A drawing made with these symbols is called a c i rc ui t d i agra m.
You can use the symbols in Table 11.2 to draw and interpret
circuit diagrams (Figure 11.26). Knowing the basic circuit symbols
can help you analyze existing circuits and make it easier to
understand where the current flows and how a device functions.
Follow these rules when you draw circuit diagrams.
• Always use a ruler to draw straight lines for the conducting
wires.
• Make right-angle corners so that your finished diagram is a
rectangle.
Table 11.2 Circuit Symbols
Symbol
Component
Function
wire
conductor; allows electrons to flow
cell, battery
electrical source; longer side is the positive
terminal, shorter side is the negative terminal
lamp (light bulb)
specific load; converts electricity to light and
heat
resistor
general load; converts electricity to heat
switch
opens and closes the circuit
ammeter
measures current through a device, connected
in series
voltmeter
measures voltage across a device, connected in
parallel
Learning Checkpoint
1. What is a circuit diagram?
2. What are two rules you should follow when you draw a circuit diagram?
3. Draw the circuit symbol for:
(a) a light bulb
(b) an ammeter
(c) a voltmeter
4. Draw a circuit diagram for a circuit that includes a resistor, a switch,
conducting wires, and a battery.
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Series Circuits
A s e r i e s c i rc u i t is an electric circuit in which the components
are arranged one after another in series (Figure 11.27). A series
circuit has only one path along which electrons can flow. If that
pathway is interrupted, the whole circuit cannot function.
The amount of current is the same in all parts of a series
circuit. However, if you add more resistors, you increase the total
resistance of the circuit. This decreases the current. Adding an
extra bulb to a series string of lights makes all the bulbs dimmer.
Electrons use up all their potential difference going around a
series circuit no matter how many loads are in the circuit. For
example, the electrons that leave a 12-V battery will “lose” all
12 V before they return to the battery. Each load will use part of
the total potential difference, depending on how much it resists
the flow of electrons.
Figure 11.27 A series circuit has
only one path along which current
can flow.
junction point
Parallel Circuits
A p a ra l l e l c i rc u i t is an electric circuit in which the parts are
arranged so that electrons can flow along more than one path
(Figure 11.28).
The points where a circuit divides into different paths or
where paths combine are called junction points. An interruption
or break in one pathway does not affect the other pathways in the
circuit. Similarly, adding a new pathway with more resistors does
not affect the resistance in any of the other pathways. In fact,
adding extra resistors in parallel decreases the total resistance of
the circuit. This might seem strange, but think about how much
less resistance there is when you drink through two straws
instead of one.
Most electrons will follow the path with the smallest
resistance values. Therefore, the amount of current is greater on
the paths with the smaller resistances (Figure 11.29).
Each electron has the same amount of energy, and electrons
must expend all their energy on the path they are on. This is why
the potential difference across parallel resistors will always be the
same, even though the resistors themselves are of different values.
Table 11.3 on the next page summarizes the characteristics of
current and potential difference in series and parallel circuits.
Figure 11.28 In a parallel circuit,
each component has its own path
for current.
3.0 A
2.0 A
1.0 A
6.0 A
Figure 11.29 Loads of different
resistance that are connected in
parallel have different currents.
Current electricity is the continuous flow of electrons in a closed circuit.
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Table 11.3 Potential Difference, Current, and Resistance in Series and Parallel Circuits
Circuit
Potential Difference
Current
Resistance
Series circuit
Each load uses a portion of the total
potential difference supplied by the
battery.
The current is the same throughout
a series circuit.
The current decreases
when more resistors are
added.
Parallel circuit
Each load uses all the potential
difference supplied by the battery.
The current divides into different
paths. A pathway with less
resistance will have a greater
current.
Adding resistors in parallel
decreases the total
resistance of the circuit.
Two Types of Circuits
Suggested Activities •
D17 Quick Lab on page 453
D19 Inquiry Activity on page 455
D20 Inquiry Activity on page 456
Figure 11.30 A combination circuit.
The switch in this circuit can turn all
the bulbs on or off.
What happens when one light bulb burns out in a long string of
decorative lights? If the set of lights is wired in series, the current
must flow through one light before it gets to another light. When
one light burns out, all lights go out because the current cannot flow
past a burned-out bulb.
If the set of lights is wired in parallel, the current takes several
different paths. If a light on one path goes out, current does not
flow on that path. However, there are other paths where the
current does flow and lights on those paths remain lit.
Series circuits and parallel circuits make up the circuits in
your home and school. Some circuits are combinations of series
circuits and parallel circuits (Figure 11.30). These combinations
help prevent problems such as the refrigerator turning off because
a light bulb burned out in a bedroom. It is an important safety
feature in a combination circuit to have some switches wired in
series, because it is sometimes necessary to turn off the electricity
in part or all of a home (Figure 11.31).
Figure 11.31 A typical home has
many parallel circuits.
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Learning Checkpoint
Take It Further
1. Draw a circuit diagram of a series circuit with a battery, connecting wires,
and one light bulb.
2. Draw a circuit diagram of a parallel circuit with a battery, connecting wires
and two light bulbs.
3. What happens to the voltage in a series circuit when more loads are
added?
A microcircuit is an extremely
small circuit that may contain
more than a million parts in a
square centimetre. Find out how
these tiny circuits are controlled
and used. Begin your research at
ScienceSource.
4. What happens to the current in a parallel circuit when more loads are
added?
5. How do combination circuits help prevent problems in circuits in a home?
D17 Quick Lab
Off and On
Suppose that all the lights in your home were
connected in one simple circuit. When you closed a
switch, every light would come on. When you opened
the switch, every light would turn off. This
arrangement would not be very practical for most
uses. Instead, lights can be connected in a circuit in
such a way that some can be turned on while others
are turned off. In this activity, you will investigate how
to create such a circuit.
Purpose
To design and build a circuit that can have lights
turned on and off individually
Procedure
1. Circuit A: Design and draw a circuit diagram
where the three bulbs can be either all on or all
off.
2. Circuit B: Design and draw a circuit diagram
where each of the three bulbs in the circuit can
be turned off and on individually.
3. Circuit C: Design and draw a circuit diagram
where two bulbs can be turned off while one
stays on.
4. Have your teacher approve your three circuit
diagrams. Then, hook up the circuits and test
whether they work.
5. Clean up your work area.
Materials & Equipment
Questions
• 3 or more flashlight bulbs with holders
• connecting wires
• 3 D dry cells
• switches for each light
CAUTION: Open the circuit if the wires get hot.
6. For each circuit, describe whether the lights were
hooked up in series, in parallel, or in a
combination.
7. Was the brightness of the lights affected by
changing how the bulbs were hooked up?
Explain.
Current electricity is the continuous flow of electrons in a closed circuit.
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D18 Skill Builder Activity
Using Equipment Accurately and Safely
Part 1 — Measuring Current
Measuring current involves measuring the amount of
charge passing a given point per second. The
current is fed directly into the ammeter or multimeter
where it is counted and then let back out into the
circuit. The ammeter is hooked in series into the
circuit, then the circuit is reconnected and the
measurement is taken.
Follow these steps to hook up the ammeter.
1. Attach a battery and three resistors in series.
Open the circuit.
2. Hook your ammeter in series next to the positive
side of the battery. Be sure to connect the
positive (red) terminal of the ammeter to the
positive (+) terminal of the battery. Connect the
negative (black) terminal of the ammeter to the
negative (–) terminal of the battery.
3. Set the meter on the highest setting, and then
lower the setting until you have the highest
possible reading. Record the reading.
4. Open the circuit and move the ammeter to
immediately beyond the first resistor. Repeat
steps 2 and 3.
5. Repeat step 4 for each resistor.
CAUTION: Open the circuit if the wires and resistors
get hot.
Part 2 — Measuring Voltage
6. To insert a voltmeter in a circuit, simply connect
the two wires from the terminals of the voltmeter
to opposite sides of the component for which
you want to measure the voltage (Figure 11.32).
7. To find the voltage across an electrical source,
connect the meter by attaching the red lead to
the positive terminal and the black lead to the
negative terminal. This allows you to take a
reading on both sides of the source. The meter
indicates the change in voltage.
8. To find the voltage across a resistor or load in a
circuit, connect a lead to each side of the
resistor. Connect the black lead closest to the
negative side of the source and the red lead
closest to the positive side of the source. This
method of connection is called connecting in
parallel. By measuring voltage across the
resistor, you are measuring the voltage drop as
the current moves through the resistor.
9. Your teacher will provide you with various types
of dry cells and batteries. Use the voltmeter to
test and report on the voltage of each cell and
battery. Compare your readings with the voltage
numbers that are written on their labels. If a
multimeter is available, use it to repeat your
measurements and then compare the results.
10. Hook two or three dry cells in series. Do this by
placing them end to end with the positive end of
one dry cell touching the negative end of the
other dry cell. Predict the voltage reading, and
then use the voltmeter to see if your prediction
was correct.
11. Clean up your work area.
Figure 11.32 A voltmeter connected across a resistor
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SKILLS YOU WILL USE
D19 Inquiry Activity
Skills Reference 2
Series Circuit Analysis
Question
3. Record the voltage across each resistor and the
power supply.
What are the properties of a series circuit?
4. Open the switch, and move the ammeter to a
position between the first two resistors. Close the
switch, and record the current coming out of
resistor 1.
Materials & Equipment
• 6.0-V battery
• multimeter (or
voltmeter and
ammeter)
• three 100-⍀ resistors
• switch
5. Open the switch, and move the ammeter to a
position between the second and third resistors.
Close the switch, and record the current coming
out of resistor 2.
• connecting wires
CAUTION: Open the circuit if the wires and resistors
get hot.
Procedure
Part 1 — Measuring Voltage and Current
1. Create a data table similar to the one below. Give
your table a title.
Power
Supply
Resistor
1
Planning for safe practices in
investigations
Gathering, organizing, and
recording relevent data
from inquiries
Resistor
2
Resistor
3
Part 1:
Current
6. Open the switch, and move the ammeter to a
position between the third resistor and the
source. Close the switch, and record the current
coming out of resistor 3.
Part 2 — Changing Resistance
7. Open the switch, and remove one resistor. Close
the switch. Measure and record the current.
8. Measure and record the voltage across the power
supply and across each of the two resistors.
Analyzing and Interpreting
9. State what you noticed in Part 1 about the:
Voltage
(a) current across the resistors in all cases
Part 2:
Current
(b) sum of all voltages across the resistors
10. State what happened in Part 2 to:
Voltage
(a) the current
2. Construct the circuit shown in Figure 11.33.
Keep the switch open until your teacher approves
your circuit. Then close the switch and record the
current coming out of the power supply.
A
(c) the sum of the voltages across the resistors
11. What is the effect of adding an identical load in
series in a simple circuit?
Skill Practice
12. Did the voltages across any resistors equal the
total voltage provided by the source? Explain why
they did or did not.
6.0 V
V
resistor 1
(b) the voltages across each resistor
resistor 2
resistor 3
Figure 11.33 Construct this circuit in step 2.
Forming Conclusions
13. In a paragraph, summarize the properties of a
series circuit.
Current electricity is the continuous flow of electrons in a closed circuit.
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D20 Inquiry Activity
Skills Reference 2
Parallel Circuit Analysis
Question
3. Record the voltage across each resistor and the
power supply.
What are the properties of a parallel circuit?
4. Open the switch, and move the ammeter to a
position between the first two resistors. Close the
switch, and record the current coming out of
resistor 1.
Materials & Equipment
• multimeter (or
voltmeter and
ammeter)
• 6.0-V dry cell
• three 100-⍀ resistors
• connecting wires
5. Open the switch, and move the ammeter to a
position between the second and third resistors.
Close the switch, and record the current coming
out of resistor 2.
• switch
CAUTION: Open the circuit if the wires and resistors
get hot.
Procedure
Part 1 — Potential Difference and
Current Measurements
Resistor
1
Resistor
2
6. Open the switch, and move the ammeter to a
position between the third resistor and the
source. Close the switch, and record the current
coming out of resistor 3.
Part 2 — Changing Resistance
7. Open the switch, and remove one resistor. Close
the switch. Measure and record the current.
1. Create a data table similar to the one below. Give
your table a title.
Power
Supply
Selecting instruments and
materials
Observing, and recording
observations
Resistor
3
Part 1:
Current
8. Measure and record the voltage across the power
supply and across each of the two resistors.
Analyzing and Interpreting
9. State what you noticed in Part 1 about the:
(a) current across the resistors in all cases
Voltage
(b) sum of all voltages across the resistors
Part 2:
Current
10. State what happened in Part 2 to:
(a) the current
Voltage
2. Construct the circuit shown in Figure 11.34.
Keep the switch open until your teacher approves
your circuit. Then, close the switch and record
the current coming out of the power supply.
(b) the voltages across each resistor
(c) the sum of the voltages across the resistors
11. What is the effect of adding an identical load in
parallel in a simple circuit?
Skill Practice
resistor 3
V
resistor 2
6.0 V
resistor 1
A
12. Did the voltages across any resistors equal the
total voltage provided by the source? Explain why
they did or did not.
Forming Conclusions
Figure 11.34 Construct this circuit in step 2.
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13. In a paragraph, summarize the properties of a
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11.2 CHECK and REFLECT
4. (a) Draw a circuit diagram that shows three
resistors in series.
Key Concept Review
1. Copy and complete the following chart in
your notebook.
Voltage and Current in Circuits
In a Series
Circuit
In a Parallel
Circuit
Voltage
2. (a) Draw a circuit diagram of the circuit
shown here.
Connect Your Understanding
6. You have three light bulbs, each with a
different resistor. The amount of current
through a bulb will affect how much light it
emits.
(b)
(c)
–
(c) Draw a circuit diagram that shows one
resistor in series and two resistors in
parallel.
5. Suppose two pathways in a parallel circuit
have different resistances. Will the current
in each pathway be the same? Explain.
Current
+
(a) Will the order in which you hook up the
light bulbs in series affect the intensity
of light each emits? Explain.
(a)
(d)
(b) Draw a circuit diagram that shows three
resistors in parallel.
(b) What happens when you hook up the
bulbs in parallel?
Question 2
(b) Is this a series circuit or a parallel
circuit?
(c) How do you know?
3. What is the voltage across the source in
each of these circuits?
7. Electrons in a circuit can be compared to a
group of shoppers who go out to spend
money in shops. Use this analogy or create
one of your own to explain the following.
Include a labelled diagram as part of your
answer for each one.
(a) potential difference, current, and
resistance in a series circuit
(a)
(b) potential difference, current, and
resistance in a parallel circuit
2.0 V
4.0 V
6.0 V
Reflection
(b)
12 V
12 V
12 V
8. What images or memory aids help you
remember the differences between series
and parallel circuits?
For more questions, go to ScienceSource.
Current electricity is the continuous flow of electrons in a closed circuit.
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Ohm’s Law
Here is a summary of what you
will learn in this section:
• Ohm’s law, V = IR, describes
the relationship between
potential difference, current,
and resistance.
• In a short circuit, the current
does not take the intended
path back to its source.
• Fuses and circuit breakers are
safety devices.
Figure 11.35 Potential difference, current, and resistance have the same relationship in
microcircuits in a computer circuit board like this one as they do in the wiring in homes
and offices.
A Fascination with Electricity
Figure 11.36 Georg Ohm (1789–1854)
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The circuit boards in the computers you use work because of the
relationships between potential difference, current, and resistance
(Figure 11.35). These relationships have been understood for about
200 years because of the work of Georg Ohm.
Georg Simon Ohm (Fig 11.36) was like any German boy in
the early 1800s. At the local high school, he studied physics,
chemistry, math, and philosophy. He spent most of his free time
playing billiards, ice skating, and dancing with his friends. No
one imagined that one day he would be a famous name in
science.
His journey to discovering a scientific law began after
graduation when he went to a private school in Switzerland to
teach. Here Ohm taught mathematics, but secretly he dreamed
of studying with great mathematicians at an important
university.
To achieve his dream, he continued to study mathematics and
teach. One day, he was asked to instruct in the electricity labs.
This day was a turning point in Georg Ohm’s life. Fascinated by
electricity, he immersed himself in the study of the characteristics
of potential difference, current, and resistance.
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Ohm’s passion and commitment to his studies led to a deep
understanding of how these different electrical concepts were
related. Much of what he discovered you have already learned in
this unit. He stated these discoveries in what is today called
Ohm’s law.
A law in science is a generalization based on collection of
observable evidence. It is the conclusion of this evidence and can be
defended by repeating a variety of experiments over many years. A
scientific law becomes accepted by the scientific community as a
description of our natural world.
Ohm’s law established the relationships between potential
difference (V ), current (I), and resistance (R). The symbol for
resistance is called the ohm (⍀) in honour of Georg Ohm’s work
in this field.
W O R D S M AT T E R
The symbol “I ” is used for current
because it stands for “intensity.”
D21 Quick Lab
Potential Difference, Current, and Resistance
Using the equipment available in your science class,
you can investigate the same relationships between
potential difference, current, and resistance that
Georg Ohm did over 200 years ago.
Purpose
To observe how potential difference, current, and
resistance are related
Procedure
1. Create a table like the one below to record the
data you will collect. Give your table a title.
2. Connect one resistor into a simple circuit. If you
are using a voltmeter and ammeter, connect
these devices as well. Keep your circuit open
until your teacher has approved your set-up.
3. Close your circuit.
4. Measure and record the voltage across the
resistor.
Materials & Equipment
5. Measure and record the current through the
resistor.
• 1.5 V dry cell
• resistors, any values from 15 ⍀ to 50 ⍀
• connecting wires
6. Record the resistance of the resistor you used.
• switch
7. Repeat steps 2 to 6.
• multimeter or voltmeter and ammeter
Trial
1.
Resistance
(⍀)
Current
(A)
Potential
Difference
(V)
8. Clean up your work area.
Resistance
ⴛ Current
Question
9. Multiply the resistance by the current for each of
the trials you completed. What can you infer from
your answers?
2.
Current electricity is the continuous flow of electrons in a closed circuit.
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Potential Difference, Current, and Resistance
I
V V
R
V = IR
Figure 11.37 Ohm’s law states that
potential difference (V) equals
current (I) times resistance (R).
Suggested Activities •
D23 Inquiry Activity on page 465
D24 Inquiry Activity on page 466
Practice Problems
1. A current of 1.5 A flows
through a 30-⍀ resistor
that is connected across a
battery. What is the
battery’s voltage?
2. If the resistance of a car
headlight is 15 ⍀ and
the current through it is
0.60 A, what is the voltage
across the headlight?
3. The current in a circuit is
0.50 A. The circuit has two
resistors connected in
series: one is 110 ⍀ and the
other is 130 ⍀. What is the
voltage in the circuit?
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Georg Ohm described how potential difference and current are
affected when one of the values is changed. He realized that the
potential difference (V) in a circuit is equal to the current (I)
multiplied by the resistance (R). Ohm’s law states that, as long as
temperature stays the same, V = IR (Figure 11.37). In other words:
• the resistance of a conductor remains constant
• the current is directly proportional to the potential
difference
Table 11.4 and the following examples show how to use
Ohm’s law to calculate unknown quantities.
Table 11.4 Ohm’s Law
Known
Quantity
Symbol
Unknown
Quantity
Symbol
Unit
Equation
Current,
resistance
IR
potential
difference
V
V
V = IR
Potential
difference,
resistance
VR
current
I
A
I=V
R
Potential
difference,
current
VI
resistance
R
⍀
R=V
I
Example Problem 11.1
A current of 4.0 A flows through a 40-⍀ resistor in a circuit.
What is the voltage?
Given
Current I = 4.0 A
Resistance R = 40 ⍀
Required
Voltage V = ?
Analysis and Solution
The correct equation is V = IR.
Substitute the values and their units, and solve the problem.
V = IR
= (4.0 A)(40 ⍀)
= 160 V
Paraphrase
The voltage in the circuit is 160 V.
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Example Problem 11.2
Practice Problems
A 30-V battery generates a current through a 15-⍀ resistor.
How much current does the battery generate?
Given
Voltage V = 30 V
Resistance R = 15 ⍀
Required
Current I = ?
1. A firetruck has a
searchlight with a
resistance of 60 ⍀ that is
placed across a 24-V
battery. What is the
current in this circuit?
2. A bulb of 15-⍀ resistance
is in a circuit powered by
a 3-V battery. What is the
current in this circuit?
Analysis and Solution
The correct equation is I = V .
R
Substitute the values and their units, and then solve the
problem.
I=V
R
3. What would the current
be in question 2 if you
changed to a 45-⍀ bulb?
= 30 V = 2 A
15 ⍀
Paraphrase
A current of 2 A is generated.
Example Problem 11.3
Practice Problems
An electric stove is connected to a 240-V outlet. If the current
flowing through the stove is 20 A, what is the resistance of the
heating element?
Given
Voltage V = 240 V
Current I = 20 A
1. A current of 0.75 passes
through a flashlight bulb
that is connected to a
3.0-V battery. What is the
bulb’s resistance?
2. A current of 625 mA
runs through a bulb that
is connected to a 120-V
power supply. What is the
resistance of the bulb?
Required
Resistance R = ?
Analysis and Solution
V
The correct equation is R = .
I
Substitute the values and their units, and then solve the
problem.
R=V
I
= 240 V = 12 ⍀
20 A
3. A table lamp draws a
current of 200 mA when
it is connected to a 120-V
source. What is the
resistance for the table
lamp?
Paraphrase
The resistance of the heating element is 12 ⍀.
Current electricity is the continuous flow of electrons in a closed circuit.
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During Reading
Definitions in Context
Often, unfamiliar terms are
defined right in the text that you
are reading. You don’t need to
look them up in a glossary or
dictionary. Look for the
boldfaced words, and then find
the definition in the sentence
either before or after the term.
Add words and definitions to
your personal list of terms.
Quit
Ohm’s Law and Temperature
Ohm’s law works for most circuits. However, temperature affects
resistance. Generally, resistance is lower when a conductor is
cooler. As the temperature increases, resistance increases. For
example, a filament in an incandescent light bulb often has 10
times its normal current flowing through it at the instant it is
switched on. This current heats the filament white-hot in a
fraction of a second. The huge rise in temperature greatly
increases the filament’s resistance, which reduces the current
flowing through it. Light bulb filaments sometimes burn out
when they are switched on because of the sudden temperature
change and other forces caused by the large initial current.
Short Circuits
short circuit
Figure 11.38 Current can flow more
easily through the wire path than
through the light bulb. This creates
a short circuit, which could be
dangerous.
Sometimes a wire’s insulation breaks down or another problem
develops that allows electrons to flow through a device along a
different path than the one intended. The device develops a short
circuit. A short circuit is an accidental low-resistance connection
between two points in a circuit, often causing excess current flow
(Figure 11.38). Not only do short circuits mean that your
electrical device will not work, they can also be dangerous. The
conducting wires can quickly become hot and can start a fire.
One danger from short circuits occurs when a transmission
line has been knocked down in a storm. Without a complete path,
the electricity cannot flow. However, if you come in contact with
the wire, the electricity will take a path through your body to the
ground and seriously injure or kill you. The driver shown in
Figure 11.39 is safe as long as he is inside the truck. If he has to
leave, he would need to jump free, not step out. He has to jump so
he does not provide a path for the electricity to flow through him
to the ground.
There are times when a technician must short out part of a
circuit intentionally by connecting a wire across a load in parallel.
The low-resistance wire causes the current to flow through it
rather than through the higher resistance device. This allows the
technician to work on the device without interrupting the rest of
the circuit.
Figure 11.39 The driver should stay
in the truck and wait for help.
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Electrical Safety
All electrical appliances present a risk of
electric shock. Always handle electrical
appliances properly and observe all safety
precautions. Be careful to disconnect the plug
before handling an appliance. Some electronic
devices, such as computers, retain electric
charge even when they are unplugged
(Figure 11.40). This is why many electrical
devices have a “Do Not Open” warning
printed on them. Take the warning seriously,
and do not attempt to repair the device
yourself. Instead, contact a repair technician.
Fuses and Circuit Breakers
In electric circuits in your home,
fuses and circuit breakers act as a
first line of defence if something goes
wrong. A fuse is a safety device in an
electric circuit that has a metallic
conductor with a low melting point
compared to the circuit’s wires
(Figure 11.41). If the current gets too high,
the metal in the fuse melts and the current
flow stops. This prevents further problems,
such as damage to your electrical components
or a possible fire. A blown fuse must be
physically replaced as it can work only once.
The symbol
represents a fuse in a
circuit diagram.
A circuit breaker does the same job as a
fuse except that the wire inside does not melt.
Instead, the wire heats up and bends, which
triggers a spring mechanism that turns off the
flow of electricity. Once the breaker has
cooled, it can be reset. Older homes and
apartment buildings tend to have fuse panels,
whereas modern buildings have breaker
panels (Figure 11.42).
Figure 11.40 Some electronic devices, such as this computer,
store electrical energy even when the device is not plugged in.
Figure 11.41 Examples of fuses. A
normal current can pass through a
fuse, but a higher than normal
current or short circuit will melt the
metal in the fuse.
Figure 11.42 Circuit breakers help prevent electric overloads.
Current electricity is the continuous flow of electrons in a closed circuit.
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Three-Prong Plug
Another safety feature is the three-prong electrical plug shown in
Figure 11.43. The third prong of a three-prong electrical plug
connects the device to the ground wire of the building. The
ground wire sends any unwanted current flow directly to the
ground. Instead of electricity travelling to the metal body of the
device and shocking a person using the device, the current is
directed to the ground.
Ground Fault Circuit Interrupter
Take It Further
Diodes are devices that allow
electric current to flow in one
direction but not in the opposite
direction. Find out how diodes are
used in microcircuits and other
circuits. Start your research at
ScienceSource.
Some appliances and devices have an added safety feature. A
ground fault circuit interrupter (GFCI) or residual current
device is a device that detects a change in current and opens the
circuit, stopping current flow (Figure 11.44). For example, if an
appliance gets wet while you are handling it and some current
starts to flow through the water, the GFCI opens the circuit so
there is less chance of injury to you. Remember, it is extremely
dangerous to use any electrical device around water, including
radios or televisions.
Figure 11.43 One prong in a three-prong
plug carried the current to the load,
another prong returns the current to the
source, and the third prong directs the
current to the ground in the case of a
short circuit.
D22
Figure 11.44 Ground fault circuit
interrupters are part of some electric
sockets.
STSE Science, Technology, Society, and the Environment
Electrical Safety
Imagine you have just been hired as a consultant
by the Electrical Safety Authority of Ontario to
help create awareness of electrical safety for
kindergarten students.
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The Characteristics of Electricity
1. Work alone, with a partner, or in a small
group to create an electrical safety poster or
brochure that can be shared with a
kindergarten class. Be sure to choose
electrical safety points that are relevant to
young children and to communicate them in
an engaging way.
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SKILLS YOU WILL USE
D23 Inquiry Activity
Skills References 2, 10
Interpreting data/information to
identify patterns or relationships
Drawing conclusions
Investigating Ohm’s Law
Question
How are potential difference, current, and resistance
related?
3. Have your teacher approve your circuit, and then
close the switch. Quickly measure and record
current and voltage. Open the switch.
4. Replace resistor 1 with resistor 2. Repeat step 3.
5. Connect a second 1.5-V dry cell in series with the
first cell in the circuit. Repeat steps 3 and 4,
measuring current and voltage for each resistor.
Materials & Equipment
• four 1.5-V dry cells
• switch
• connecting wires
• 2 different resistors
between 100 ⍀ and
300 ⍀
• voltmeter, ammeter
CAUTION: Disconnect the circuit if the wires or resistors
get hot.
6. Connect a third 1.5-V dry cell into the circuit.
Repeat steps 3 and 4.
7. Connect a fourth 1.5-V dry cell. Repeat steps 3
and 4.
8. Calculate your measured resistance for each
.
resistor using R = V
I
Procedure
1. Set up a data table like the following. Fill in the
resistor value for the two resistors you will be
using. Examples below are 100 ⍀ and 200 ⍀.
Give your table a title.
Resistor
(⍀)
1.5 V
3.0 V
4.5 V
6.0 V
Voltage
(V)
Current
(A)
Calculated
Resistance
Analyzing and Interpreting
9. (a) How did your calculated values for resistors
compare with their actual values?
(b) Explain possible reasons for any difference
between the two values.
10. Compare your data for all resistor 1 trials. When
voltage is increased across a resistor, what
happens to the current?
1. 100
2. 200
1. 100
11. Compare your data for all resistor 2 trials. When
voltage is increased across the resistor, what
happens to the current?
2. 200
1. 100
2. 200
Skill Practice
1. 100
12. What would happen to the current values if you
used a resistor with double the value of resistor 2?
2. 200
2. Construct the following circuit using resistor 1
and one 1.5 V dry cell (Figure 11.45).
Forming Conclusions
13. Describe the relationship between potential
difference, current, and resistance.
A
V
Figure 11.45 Construct this
circuit in step 5.
Current electricity is the continuous flow of electrons in a closed circuit.
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DI Key Activity
SKILLS YOU WILL USE
D24 Inquiry Activity
Skills Reference 2
Justifying conclusions
Identifying sources of error
Resisting the Flow
Question
Do different materials have different values of
electrical resistance?
Materials & Equipment
• connecting wires
• D cell and holder
• voltmeter
• ammeter or current
sensor
• 10-cm length of solid
graphite (pencil lead)
• 10-cm length of copper
wire
• 10-cm length of
Nichrome™ wire
• 10-cm length of rubber
tubing
• optional: 10-cm
lengths of various other
materials
• calculator
CAUTION: Open the circuit if the wires or the resistors
get hot.
6. Repeat steps 4 and 5 for the copper wire,
Nichrome™ wire, rubber tubing, and the other
materials.
7. Clean up your work area.
Analyzing and Interpreting
Procedure
1. Make a table for recording your data (Figure
11.46). The table should include these headings:
Substance, Length Connected (10 cm or 1 cm),
Voltage (from step 2), Current, and Resistance. In
the “Resistance” column, you will calculate the
resistance for each observation. Give your table a
title.
2. Use connecting wires to connect each end of a D
cell to a terminal on the voltmeter. Record the
voltmeter reading in your table. Disconnect the
voltmeter.
V
to calculate the
I
resistance for each current recorded in your table.
8. Use Ohm’s law R =
9. (a) Which substance had the greatest resistance?
(b) Explain any differences in resistance among
the materials.
10. What was the effect of moving the connecting
wires so that the current travelled through a
shorter length of the conductor? Explain.
Skill Practice
3. Connect one wire from the D cell to a terminal of
the ammeter (or current sensor). Attach another
connecting wire to the other terminal of the
ammeter.
11. (a) How precise were your measurements?
4. Clip the free ends of the connecting wires onto
the ends of a 10-cm length of solid graphite.
Record the reading on the ammeter.
Forming Conclusions
5. Move the clips on the graphite so that they are
1.0 cm apart. Record any change in the reading.
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Figure 11.46 Determining resistance
UNIT D
The Characteristics of Electricity
(b) What sources of error could have affected the
accuracy of your results?
12. Write a summary that answers the question: Do
different materials have different values of
electrical resistance? Use your data to support
your answer.
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11.3 CHECK and REFLECT
Key Concept Review
Connect Your Understanding
1. (a) How is current related to potential
difference in a circuit?
8. What is the resistance in the circuit shown
here?
(b) How is current related to resistance in a
circuit?
3.0 A
2. What does Ohm’s law state?
6.0 V
3. Copy this table into your notebook, and
complete the values for potential difference,
current, and resistance in an electric circuit.
Question 8
Potential Difference, Current, and Resistance
V
I
50 ⍀
0.5 V
20 A
6.0 V
9. A 12-⍀ light bulb is in a series circuit
powered by a 6.0-V battery.
R
(a) What is the current in the circuit?
100 ⍀
(b) If you changed the 12-⍀ bulb to a 24-⍀
bulb, what current would be drawn
from the battery?
4.0 A
4. What is each of these meters called?
10. (a) If a 36-⍀ bulb is added in series in the
circuit in question 9(a), what is the
current in the circuit?
(a)
(b) What is the potential difference across
each bulb?
11. In a circuit where voltage is kept constant,
state what happens to current if resistance is:
(b)
(a) doubled
(b) quadrupled
12. (a) Why is a ground fault circuit interrupter
necessary for electrical devices that are
used around water?
5. What does each meter in question 4
measure?
6. Draw labelled circuit diagrams to show how
each meter in question 4 is connected in a:
(a) series circuit
(b) List three devices that should include a
ground fault circuit interrupter.
Reflection
(b) parallel circuit
13. What questions about electricity would you
like to have answered?
7. (a) What is a fuse?
(b) What is a fuse used for?
(c) If a fuse melts, does it create an open
circuit, a closed circuit, or a short circuit?
For more questions, go to ScienceSource.
Current electricity is the continuous flow of electrons in a closed circuit.
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CAREERS
in Science
Great CANADIANS in Science
Max Donelan
Investigating
Award-winning Canadian scientist Dr. Max
Donelan walks down many different scientific
paths. In fact, walking is something he would like
to help more people be able to do. While most
healthy people find walking a simple matter, many
individuals who suffer from paralysis due to a
stroke find that any kind of walking can be one
step too far.
A stroke is a medical condition that occurs when
a blood vessel in the brain leaks. This leakage of
blood causes brain and nerve damage. For
example, the damage can make it difficult to use
the muscles on one side of the body while the
other side is not affected at all. A person who has
had a stroke may be able to walk but may find that
he or she needs to use much more energy than a
healthy person to do the same amount of walking.
Dr. Donelan is working to find out why.
Dr. Donelan and his colleagues at Simon Fraser
University in British Columbia are studying the
science behind the way healthy people walk. They
will use the results of their studies to design
devices and strategies to help patients use energy
efficiently and regain as much mobility as possible.
Even healthy people may benefit from his
research. In studying the energy requirements
involved with walking, Dr. Donelan’s team has
come up with a device that is able to capture
energy that is generated when a person walks
(Figure 11.47). His device assists the movement
of leg muscles while generating electricity at the
same time. This is called “harvesting” energy.
Harvesting usually refers to gathering in crops like
grains or vegetables when they are ripe. In this
case, the crop is energy!
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UNIT D
The Characteristics of Electricity
Figure 11.47 Dr. Donelan watches his device in use. It is
strapped to the knee of this walker. For every minute of
walking you do, the device harvests enough electrical energy
to power a cell phone for about 30 minutes.
Dr. Donelan’s team is working to design an
energy harvester that is lightweight, slim, and
barely noticeable when worn. Being able to
produce your own electricity is useful to people in
locations where a constant electrical power supply
is not available, such as hikers and emergency
crews. In the field of energy efficiency, Dr. Donelan
is clearly a step ahead.
Questions
1. What does it mean to “harvest” energy?
2. ScienceSource Research to find out what
possible applications a human-powered
energy harvesting device could have in one
of the following fields:
• medicine
• public safety
• the military
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Science in My FUTURE
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Line Installers and Repairers
Are you ready for a career challenge? Suppose
your job description included climbing a telephone
pole at night during a snowstorm when the power
was out — in fact, you would be climbing the pole
because the power was out?
Electrical energy is an essential part of our
society, and waiting for a storm to end is not
usually an option when the power grid goes down.
Line installers and repairers are sent out often
during a summer lightning storm or a winter
freeze-up to keep electricity flowing to homes and
businesses (Figure 11.48).
As a line installer, you would do more than
make sure the lines were properly connected and
repaired. Line installing and repair includes
working with electronics and telecommunications,
such as telephone, Internet, and cable television
lines. New construction, which involves putting up
poles or burying cables, means you are likely to
use a variety of equipment, such as diggers,
trench makers and tunnelling machines. Although
machines would help you lift and carry, you would
need to be strong and physically fit. Climbing to
high places and working with high voltage carry a
definite risk, so an attitude of being careful and
working safely is essential. You might set up
service in homes for customers, so good people
skills are also an asset.
For a career as a line installer and repairer, high
school completion that includes algebra and
trigonometry is an asset, as are the kinds of
practical skills learned in shop classes.
Community colleges and technical schools often
offer programs in electricity, electronics, and
telecommunications. These programs frequently
partner with companies in the local community to
offer hands-on field work.
Figure 11.48 A line installer needs a good understanding of
electrical safety.
Even our increasingly wirelessly connected
world, we will still need tough, smart, cautious,
and strong individuals to keep the grid working
properly.
Questions
1. List four qualities that would be an asset for a
person interested in work as a line installer or
repairer.
2. ScienceSource There are many careers
related to electrical technologies, including
electricians, power plant operators, and radio
and telecommunications equipment
installers and repairers. Select one of these
or another related field, and summarize what
the job involves, the education and training
needed, and one aspect of the job that is
particularly interesting to you.
Current electricity is the continuous flow of electrons in a closed circuit.
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11 CHAPTER REVIEW
ACHIEVEMENT CHART CATEGORIES
t Thinking and investigation
k Knowledge and understanding
c Communication
7. Assume that each resistor in a circuit is of a
different value. What type of circuit does
each of the following statements describe:
series or parallel? k
a Application
Key Concept Review
(a) The voltage is the same across every
resistor.
3.0 A
(b) The voltage varies across each resistor.
4.0 V
(c) The current varies through each resistor.
(d) The current remains constant
throughout the whole circuit.
V1
9.0 V
A1
8. A current of 1.5 A flows through a 30-⍀
resistor that is connected across a battery.
Find the voltage of the battery. a
Question 1
1. (a) Is the circuit above a series circuit or a
parallel circuit? k
(b) List all the parts of the circuit above.
9. A 120-V outlet has an appliance that draws
10 A connected to it. What is the resistance
of the appliance? a
k
(c) What is the voltage at V1 in the circuit
above? k
(d) What is the current at A1 in the circuit
above? k
2. Draw a circuit diagram of a circuit that
includes a battery, an ammeter, and a light
bulb with a voltmeter, all properly
connected together. c
(c) 650 mA = ____ A
11. (a) What is the value of a resistor that
transforms 2.0 mA of current when it is
connected to a 6.0-V battery? a
(b) Reformulate question (a) twice. In the
first question, make voltage the
unknown. In the second question, make
current the unknown. a
4. (a) What happens to all light bulbs in a
series circuit when one burns out? k
(b) How does the situation change when
the lights are hooked up in parallel? k
Connect Your Understanding
5. Are circuits in a home connected in series,
in parallel, or in combinations? Explain
your answer, using examples of actual
rooms in your home. k
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(a) 1.6 MV = ____ V
(b) 1500 W = ____ kW
3. How is a parallel circuit different from a
series circuit? k
6. What is the difference between an open
circuit, a closed circuit, and a short circuit?
10. Copy and convert each of the following
units in your notebook: a
12. The word “circuit” means a complete path.
Draw and label a real-life, non-electric
example of: c
(a) a series circuit
k
(b) a parallel circuit
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13. Explain the reasons for each of these safety
rules. a
(a) Do not poke a knife into a plugged-in
toaster to clear out bread crumbs.
15. What are two ways you could increase
current in a circuit? t
16. Why does an electrical cord on a lamp not
heat up when the light bulb filament does?
(b) Avoid using an extension cord that is
thinner than the cord you are attaching
to it.
(c) When disconnecting an appliance, pull
the plug, not the cord.
(d) Do not plug many electrical cords into
one outlet.
t
17. You want to find the value of an unlabelled
resistor. You have a voltmeter, an ammeter,
wires, and a battery. How could you find
the value of the resistor accurately? t
Reflection
18. (a) What do you think is the most useful
information you learned in Chapter 11?
Why? c
(e) Do not use a kite, stick, pole, etc. close
to an overhead wire.
(f) Make sure your hands are dry before
touching any electrical device, cord,
plug, or socket.
(b) How might you put your understanding
of this information to practical use? c
(g) Never use a frayed electrical cord.
After Reading
14. (a) What is dangerous about the situation
shown in the picture below? a
(b) What should the worker do to be safer?
Reflect and Evaluate
a
(c) The drill is plugged into the wall with a
three-prong plug. How does the third
prong on the plug act as a safety
mechanism? k
With a partner, list all the ways that this chapter
supports understanding of unfamiliar terms.
Revisit your personal list of terms and definitions.
Which terms are now more familiar to you? Which
terms might you need to review? What strategies
will best help you to review those terms? Create
two study goals for this chapter based on your
understanding of terms.
Unit Task Link
In this chapter, you set up series and parallel
electric circuits that could light one or more light
bulbs. An electrical grid composed of several
generating stations and a number of communities
is a complex electrical circuit. However, many of
the basic principles you have learned about
simple circuits apply to it. Consider how series
and parallel circuits might be used to supply
electricity from two generating stations to three
communities. Sketch a simple circuit that would
connect all three communities to both generating
stations so that each community has a reliable
source of electricity.
Question 14
Current electricity is the continuous flow of electrons in a closed circuit.
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12
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UNIT D
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We can reduce our electrical energy
consumption and use renewable energy
resources to produce electrical energy.
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Skills You Will Use
Wind turbines can share the land with crops or
grazing animals. A number of wind turbines are often
connected together in “wind farms” to produce
electrical energy.
In this chapter, you will:
• determine the energy consumption and operating costs of
various appliances
• calculate the efficiency of an energy converter
Concepts You Will Learn
In this chapter, you will:
• assess social, economic, and environmental effects of
producing electricity from renewable and non-renewable
sources
• produce a plan of action to reduce electrical energy
consumption at home and outline the responsibilities of
various groups in this project
Why It Is Important
We are using up non-renewable resources more rapidly than
ever before to generate electricity. Now is the time to change
this cycle. Your knowledge of electricity can help you make
intelligent choices and understand complicated debates
about global energy issues.
Before Writing
Get Your Reader’s Attention
Good writers want you to be interested in what they
have to say. They often use the opening sentence in a
paragraph as a hook to get you reading further.
Survey the first paragraph under each main
subheading in chapter 12, and decide which one best
grabs your attention.
Key Terms
• efficiency • hydroelectricity • kilowatt-hours
• non-renewable resources • renewable resources
• sustainability • thermoelectric generating plant
• thermonuclear
We can reduce our electrical energy consumption and use renewable energy resources to produce electrical energy.
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Renewable and Non-Renewable Energy
Resources for Generating Electricity
12.1
Here is a summary of what you
will learn in this section:
• Electrical generators transform
the energy of motion into an
electric current.
• Most electricity generated in
Canada is from hydroelectric or
thermoelectric sources.
• Other energy sources include
biomass, geothermal energy,
sunlight, wind, and tides.
• There are both renewable and
non-renewable energy sources.
• Every energy source has both
pros and cons.
• We need to move toward
sustainability in our use of
resources.
Figure 12.1 Students in Elliot Lake helped install solar energy panels on their school for
generating electricity.
Local Solutions to Generating Electricity
N
Elliot Lake
Thunder
Bay
0
50 100 km
Sudbury
Sault Ste. Marie
Ottawa
Toronto
Windsor
Figure 12.2 Location of the town of
Elliot Lake
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UNIT D
When you turn on the light in your bedroom, you are using
electricity that was generated far from your home. A large
hydroelectric dam, a coal-burning generating plant, or a nuclear
generating plant is probably the source of your electricity. In some
areas of Ontario, the source is wind farms made up of giant wind
turbines. To build a hydroelectric dam or enough wind turbines
to generate electrical energy for a large number of people requires
a huge investment in money, people, and equipment. Usually,
governments and businesses build these large-scale projects.
Coal and oil are non-renewable resources. A non-renewable
resource is one that cannot be replaced once it is used up. However,
in the past 10 years, governments have invested small-scale projects
that use other sources of energy, such as the Sun, to generate
electrical energy. The Sun and the wind are renewable resources.
A renewable resource is one that can be reused or replaced.
In some parts of Ontario and elsewhere in Canada, renewable
energy sources can be a practical alternative to non-renewable
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resources for generating electrical energy to meet specific
needs in communities.
Elliot Lake Secondary School is one example of a small
renewable energy project (Figure 12.1). Students at the
school proposed to the government that they would place
12 solar panels and a wind turbine on the roof of their
school. They pointed out that the electricity generated from
these two energy sources would help provide electricity to
the school. The project also supported the community of
Elliot Lake’s program to reduce its dependence on nonrenewable energy sources such as coal and oil (Figure
12.2). Impressed with the students’ ideas, the government
of Ontario awarded them a $50 000 grant. Figure 12.1
shows students at the school installing solar panels at the
school. Now the students also have work experience related
to installing solar panels and wind turbines.
All over Ontario and Canada, communities are
developing small-scale projects to produce electrical energy
using renewable energy methods (Figure 12.3).
Figure 12.3 The GreenWorks Building at the
Kortright Conservation Centre in Toronto
generates electricity using solar energy.
(© Toronto and Region Conservation, all rights
reserved)
D25 Quick Lab
Renewable Energy Projects in Your Community
Renewable energy projects can be found all over
Ontario. Using print and electronic resources, you
and your classmates will learn about examples of
these projects in your community.
Purpose
To identify and describe the function of renewable
energy projects in your community
Materials & Equipment
• information summaries about renewable energy
projects
2. With a partner or small group, select one project
to work on.
3. Create a summary of the key features of the project
— type of technology used, reason for the project,
costs, and value to users and the community.
4. Present your findings to the class.
Questions
5. How many different kinds of renewable methods
for generating electricity did you discover?
Procedure
6. Are some methods of generating electricity more
common than others? Why do you think this is
the case?
1. Your teacher will provide summaries of projects
using renewable resources for generating electrical
energy in your area or elsewhere in the province.
7. What do you think is one reason there are not
more renewable energy projects in your
community?
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Generating Electricity
Figure 12.4 Michael Faraday
(1791–1867)
W O R D S M AT T E R
A turbine converts steam or moving
water to mechanical energy using
paddles or fins or even buckets. The
word “turbine” comes from the Latin
turbo, meaning spinning top or
whirlwind.
In 1831, an English chemist and physicist named Michael
Faraday made an electrical discovery that changed the world
(Figure 12.4). Faraday introduced a way to generate a steady
supply of large amounts of electricity. He demonstrated that an
electric current can be generated by moving a conducting wire
through a magnetic field, a process called electromagnetic
induction.
We use electromagnetic induction today to generate electricity
in large-scale generators (Figure 12.5). Most generators do the
same job: they transform the energy of motion into an electric
current. The magnets inside a generator are rotated by a turbine,
which is a machine that uses the flow of a fluid to turn a shaft.
The magnets spin coils of copper wire. This pulls electrons away
from their atoms and creates a current flowing in the copper wire.
The current is sent through transmission lines to reach cities
and towns. The web of interconnections between generating
stations, substations, and users is called an energy grid or a
distribution grid (Figure 12.6). Generating electricity starts with
a spinning turbine and ends up at your wall socket. But where
does the energy come from to spin the turbine?
Figure 12.5 The electricity we use in
our homes and schools is produced
by massive coils of wire rotating
between magnets in huge
generators, like this one in
Nanticoke, Ontario.
transmission line
generating
station
underground
power wires
substation
Figure 12.6 An electric power grid
transfers energy from the generating
stations to the users. The whole grid
is a complete circuit.
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Using Water Power to Generate Electricity
Most electricity generated in Canada is hydroelectricity, which
means it is generated by harnessing the power of flowing water.
Some hydroelectric stations in smaller communities use
fast-flowing rivers to turn their turbines. Other hydroelectric
stations, such as the ones at Niagara Falls, use the flow from a
waterfall to turn their turbines (Figure 12.7).
Most communities do not have a waterfall, so a dam may be
built across a river to store water in a reservoir. The water is then
directed through a channel called a penstock to a turbine with
ridges around it (Figure 12.8). The water turns the turbine,
which is connected to a generator.
During Writing
Show What You Know
As a writer, you want to
convince a reader that you know
your topic. Add details, use
facts, and present evidence to
demonstrate your knowledge.
W O R D S M AT T E R
The prefix “hydro-” comes from the
Greek word hudor, which means
water.
Figure 12.7 The Sir Adam Beck
Generating Station at Niagara Falls
generator
transformer
water flow
penstock
turbine
Figure 12.8 In a hydroelectric generating station, water flows
through a penstock. As it flows past the turbine, it causes the
turbine to turn. The turning turbine is connected to the
generator. The generator converts the energy from the turning
motion of the turbine to electrical energy.
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W O R D S M AT T E R
The combining forms “therm-” and
“thermo-” are from the Greek word
for heat.
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Using Heat to Generate Electricity
If there are no waterfalls or rivers in your area, what mechanical
force can be used to turn the turbines? One answer is steam. In
many areas, thermoelectric generating plants use a fuel such
as coal or biomass to heat water to create high-pressure steam.
Fossil Fuels
Coal, oil, and natural gas are fossil fuels, which means they were
produced from the organic matter of organisms that lived millions of
years ago. A fossil fuel, usually coal, is burned in a generator to boil
water. The steam is kept under great pressure in pipes, which allows
it to reach higher temperatures than normal. The high-pressure
steam strikes and pushes the blades on the turbine (Figure 12.9).
coal in
combustion
chamber
cooling tower
condenser
water
exhaust steam
high-pressure steam
turbine
generator
transformer
Figure 12.9 A coal-fired generating station
Biomass
Figure 12.10 Corn husks are an
example of biomass that is burned
to boil water to make steam to turn
a turbine.
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Biomass is organic material made up of plant and animal waste.
Examples of biomass include wood, peat, straw, nut shells,
sewage, and corn husks (Figure 12.10). In a biomass system, the
organic waste decomposes to produce a gas called methane. The
methane gas can be burned to boil water to make steam. The most
common biomass material used today is wood waste from lumber
and from pulp and paper industries.
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Nuclear Energy
Ontario requires a huge amount of
electrical energy. We have a large
population and are a major centre of
manufacturing. Our electrical energy
needs far surpass what hydroelectric and
thermoelectric generators supply. Fiftyone percent of our electricity in Ontario is
thermonuclear, which means it is
produced by heat in nuclear power
stations (Figure 12.11).
In a nuclear reactor, atoms of a heavy
Figure 12.11 The Pickering Nuclear Power Plant is one of three nuclear
generating stations in Ontario.
element, usually uranium, are split in a
chain reaction. This splitting, called
nuclear fission, releases an enormous amount of energy. The
nuclear fission of just 1 kg of uranium is equivalent to burning
about 50 000 kg of coal. The energy released by the fission process
is used to heat water to produce steam to turn a turbine.
Geothermal Energy
In some places in the world, water is naturally heated by hot rock
deep in Earth’s crust and rises to the surface as hot water and steam
(Figure 12.12). The energy from this hot water and steam is called
geothermal energy. Geothermal energy sources at or near Earth’s
surface are hot enough to heat homes and other buildings. For
generating electricity, hotter sources are needed.
High-temperature geothermal sources are found deep in areas
where there is volcanic activity. Iceland has active volcanoes and
many hot springs. It uses geothermal energy to produce 19 percent
of its electricity. In Canada, geothermal sources hot enough to be
used to drive turbines for electricity generation are located in
British Columbia. Tests are under way there to determine how to
use geothermal sources cost effectively.
Figure 12.12 A hot spring is an
example of geothermal energy.
Learning Checkpoint
1. What is a non-renewable resource?
2. What does a generator do?
3. What is a turbine?
4. What source does most of Canada’s electricity come from?
5. What is a fossil fuel?
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Other Energy Sources
There are other energy sources that can be used to generate
electricity. As different technologies continue to be developed and
refined, our ability to use these sources economically increases.
Solar Energy
Many people think solar cells are a new technology, but the roots
of this invention go back to 1839, when French scientist Edmond
Becquerel soaked two metal plates in an electricity-conducting
solution. When Becquerel exposed one of the plates to sunlight,
he could detect a small potential difference between the plates. He
had invented the first solar cell. Scientists now make solar cells
using silicon (Figure 12.13).
sunlight
A
A Protective cover glass
B
B Antireflective coating to let light in and trap it
C
D
C Metal contact grid to collect electrons for circuit
E
D Silicon layer to release electrons
F
Figure 12.13 A solar cell has
E Silicon layer to absorb electrons
F Metal contact grid to collect electrons from circuit
specially treated layers that create
current when exposed to sunlight.
Solar modules (several cells connected together) and arrays
(several modules) have many uses, including powering
calculators, lights in telephone booths, and the International
Space Station. A solar farm includes arrays of mirrors that focus
sunlight onto a liquid that is heated and used to turn water into
steam to drive the turbines (Figure 12.14). One of the world’s
largest solar energy projects includes solar farms in Sarnia and
Sault Ste. Marie and aims to produce enough electricity for about
9000 homes.
Figure 12.14 The mirrors in this
solar array focus heat from the Sun
on a container that is part of a
system to turn water into steam.
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Wind Energy
Wind turbines use the energy of moving air to spin their blades,
which are connected to a generator (Figure 12.15). The amount
of energy a wind turbine generates depends on how fast the wind
is blowing, with approximately 10 km per hour being the
minimum for power generation.
In Ontario, the wind blows strongly enough, on average, about
20 percent of the time, but in some areas of Canada and the
world, winds are stronger and more consistent. Wind energy
currently provides about 1 percent of Ontario’s electricity, but it
is one of the fastest-growing energy sources in the world.
Tidal Energy
Tidal energy uses the energy of the gravitational pull of the
Moon. North America’s only tidal power generating station is in
Annapolis Royal, in Nova Scotia, where the powerful tides of the
Bay of Fundy spin its turbines (Figure 12.16). The station
provides enough electricity for about 4500 homes.
Tests are under way in British Columbia and Nova Scotia for a
promising new technology called a tidal stream generator, which
works like an underwater windmill. Other marine energy sources
that are being tested include ocean wave energy and ocean
thermal energy.
Figure 12.15 A wind farm near
Shelburne, Ontario
Figure 12.16 This tidal power station in Nova Scotia generates electricity by using the
energy of the water as it rises and falls in the daily cycle of tides.
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Comparing Methods of
Generating Electricity
Relative Costs of Electricity Generation Technologies
(Canadian cents per kilowatt hour, 2003)
80
70
60
50
40
30
20
wave and marine
geothermal
wind
solar photovoltaic
large hydro
small hydro
micro hydro
landfill gas
biomass
gas
nuclear
0
coal
10
SOURCE: CERI, Relative Costs of Electricity Generation Technologies, September 2006
Figure 12.17 Relative costs of electricity generation technologies
Energy sources for generating electricity can
be grouped into two broad categories. Nonrenewable energy sources are sources that are
limited and cannot be renewed naturally.
Fossil fuels (natural gas, propane, coal, and
petroleum) are non-renewable sources, as is
uranium. Once these materials are used up,
they cannot be replaced.
Renewable energy sources are sources that
can be replenished by natural processes in a
relatively short time, such as sunlight, wind,
tides, and waves. Biomass is a renewable
source if the trees or other plants that
produce it are properly managed.
A few of the advantages and
disadvantages of using different energy
sources are summarized in Table 12.1 and
Table 12.2. A comparison of the approximate
costs of using each source is shown in
Figure 12.17.
Table 12.1 Some Advantages and Disadvantages of Non-Renewable Sources
for Electricity Generation
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Source
Some Advantages
Some Disadvantages
Fossil fuels
– Fossil fuel generating
stations can quickly adjust
to changes in electricity
demand.
– The technology for using
these fuels is already in
place.
– The burning of fossil fuels
releases pollutants into the
atmosphere and directly
contributes to global
warming.
– Mining coal is hazardous to
workers and damages the
environment.
Nuclear
– Nuclear power is
inexpensive to produce.
– Nuclear power produces
enormous amounts of
energy from very little fuel.
– Nuclear waste is poisonous
and radioactive and needs
to be stored very carefully
for hundreds or thousands
of years.
– Nuclear plants are very
costly to construct and to
maintain.
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Table 12.2 Some Advantages and Disadvantages of Using Renewable Sources
for Electricity Generation
Source
Some Advantages
Some Disadvantages
Flowing water
(hydroelectricity)
– Large hydroelectric
generating stations produce
electricity inexpensively.
– Reservoirs may be used for
flood control, irrigation,
drinking water, and
recreation.
– Small-scale hydroelectric
plants using local rivers
can be practical for some
communities (Figure
12.18).
– There is a huge
environmental impact when
a dam is constructed,
including flooding large
areas of land, disruption or
destruction of wildlife and
fish habitat and migration
routes, and displacement of
Aboriginal and other
communities.
– Hydroelectric stations are
very expensive to build.
Sunlight
– Solar cell energy is a
convenient source of
energy for small
appliances, such as
calculators.
– Solar energy is useful in
remote areas.
– Solar cell efficiency is low,
so many photoelectric cells
have to be used, which
takes up large areas of
land.
– Solar energy is the most
expensive energy source at
present.
Tides
– Once tidal generating
stations are built, tidal
energy is very inexpensive.
– Tides are more predictable
than wind or sunlight.
– The environmental impact
on marine life in area can
be significant, due to
changes in water level and
water quality.
– Tidal energy is suitable for
few areas as it requires very
high tides.
– Wind energy production
does not produce
greenhouse gases that
contribute to global
warming.
– Farming and grazing can
continue on land where
wind turbines are located.
– The wind does not always
blow or remain constant.
– Wind turbines can present
barriers to bird movement,
cause bird fatalities due to
collisions with turbine
blades, and can disturb
breeding, wintering, and
staging sites.
Wind
Figure 12.18 Small-scale
hydroelectric generating stations
can be a local source of electrical
energy.
Suggested STSE Activity •
D26 Decision-Making Analysis Case
Study on page 486
Learning Checkpoint
1. What are three applications of solar cells?
2. What does a wind turbine do?
3. What is one of the fastest-growing energy sources in the world?
4. How is electricity generated from tides?
5. How is a renewable energy source different from a non-renewable energy
source?
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Electrical Energy Production in Canada
Take It Further
Hydrogen may be our fuel of
choice in the future. It can be
burned like other fuels or
converted into electricity in fuel
cells. Find out how the most
abundant element in the universe
can be put to use for our electrical
needs. Start your research at
ScienceSource.
Canada is the world’s largest producer of hydroelectricity,
the fifth-largest producer of electricity in general, and the
second-largest exporter of electricity.
However, we need to be aware of the environmental
implications of using non-renewable resources. As Figure 12.19
shows, a large part of our electricity is generated using
non-renewable resources. These resources include coal, uranium
(for nuclear energy), oil, and gas. We must decide how to make a
transition to using more renewable resources. We need electricity,
but we also need to generate it wisely.
All of our energy sources are important to Canada because
they provide us with flexibility and energy security and help us to
become self-sufficient. For example, at one time, Prince Edward
Island was completely dependent on outside sources for
electricity because it does not have fossil fuels, hydroelectricity, or
nuclear power. However, the island now produces 18 percent of
its electricity from wind energy and has become the first place in
North America to offer a guaranteed price to anyone — even a
homeowner — who produces electricity from wind power.
In Ontario and across Canada, renewable energy projects for
generating electricity are under way or being planned. However,
as you can see in Figure 12.19, this type of electricity generation
produced only 0.6 percent of our electricity in 2007. It cannot
replace our use of non-renewable energy resources for now. To
reduce our use of non-renewable resources, we have to find
ways to use less electricity through technology and changing our
usage habits.
Electricity Generated in Canada 2007
14.6
4.0
0.6
60.1
20.7
hydro
nuclear
coal
oil and gas
Figure 12.19 Methods of electricity generation in Canada
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A Sustainable Choice
Choosing the right methods for generating electricity means
finding sustainable solutions. Sustainability means using
resources at a rate that can be maintained indefinitely. If we do
not achieve sustainable energy use, future generations in Ontario
may not be able to support themselves.
A sustainable approach sometimes requires a different way of
using resources. Sustainability may mean no longer using nonrenewable resources because they cannot be maintained
indefinitely. In the past, fossil fuels were used up as quickly as
possible to earn money and satisfy consumer demand. We need to
use our resources in a way that makes them available over a
longer period of time. With renewable energy methods, resources
such as solar energy and wind are available indefinitely.
Figure 12.20 shows the main methods worldwide for
generating electricity in 2007. Coal, oil, and gas account for
66.6 percent of electricity production. These three methods are
using non-renewable resources. The other three methods, hydro,
nuclear, and other account, for 33.4 percent of the production.
Hydro and other methods use renewable energy sources.
We may never be able to achieve complete sustainability, but the
decisions we make personally and as a society can move us closer to
this goal. An example of a personal decision would be to turn off the
lights in your bedroom or classroom if you are the last person out of
the room. This small action would save on electrical use. As you get
older, you may make bigger decisions such as adding solar panels to
a house you live in (Figure 12.21). Decisions such as these
demonstrate you are keeping the goal of sustainability in mind.
Suggested Activity •
D27 Decision-Making Analysis on
page 488
Figure 12.21 The people who live in
this house are using solar panels to
heat their water. This reduces their
electricity use.
Electricity Generated Worldwide in 2007
2.2
19.7
16.0
40.3
6.6
15.2
hydro
nuclear
gas
coal
oil
other
Figure 12.20 How the world generates electricity. This graph could become very different
during your lifetime.
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CASE STUDY
D26
STSE Decision-Making Analysis
SKILLS YOU WILL USE
Skills Reference 4
■
■
Drawing conclusions
Justifying conclusions
Three Gorges: Potential Disaster or Good Choice?
Issue
The Three Gorges Dam on the Yangtze River in
China is the world’s largest hydroelectric generating
station (Figure 12.22). The dam is 2.3 km long and
101 m high, with a reservoir that floods 632 km2 of
land. The dam provides electricity to nine provinces
in China. Is the electricity the dam provides worth the
problems it causes?
Background Information
Two students, Bassim and Kara, have been
researching the Three Gorges Dam to find out the
costs and benefits of this huge hydroelectric project.
The more they have learned about the dam, the
more they are convinced of their own viewpoints.
Kara’s Viewpoint: In Favour of the Dam
The Three Gorges Dam is a good example of China’s
commitment to using renewable resources to
increase its production of electricity.
• Until recently, 82 percent of China’s electricity
was generated in coal-burning stations. Three
Gorges could allow China to reduce coal
consumption by 31 million tonnes per year,
so millions of tonnes of greenhouse gases
and pollutants will not be created.
• China plans to increase electricity from
renewable resources from 7.2 percent to
15 percent by 2020. A series of smaller
dams being built on the Yangtze will reduce
silt and help to maximize the efficiency of
the Three Gorges Dam.
• China is taking steps to minimize
environmental damage. Billions of dollars
already have been spent in water clean-up
projects and in preventing landslides.
• The potential of the dam to prevent or
reduce flooding for the millions of residents
downstream means that far more lives and
property can be saved than were lost due to
the building of the dam.
• As well as providing flood control, the dam
has improved navigation so that large ships
can travel farther upriver, improving the
economy of the area.
• The people of China need more electricity,
and they have made a good choice in using
renewable sources.
Figure 12.22 The Three Gorges Dam provides electricity to nine Chinese provinces. However, it has negatively affected
millions of people who used to live where its reservoir now lies.
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STSE Decision-Making Analysis (continued)
Bassim’s Viewpoint: Opposed to the Dam
The Three Gorges Dam is a social and environmental
disaster and should not have been built. Millions of
people live downstream from the dam and are in
danger if the dam should ever fail.
• Over 1.2 million people were forced out of their
homes so that their land could be flooded by the
reservoir. Many of these people have had to
move a second time due to an increase in
landslides caused by filling the reservoir. Four
million people are being encouraged to move
before 2020.
• As well as submerging homes and more than
1300 archaeological sites, the reservoir also
submerged factories, mines, and waste
dumps. All the chemicals and other waste at
those sites now contribute to the pollution of
the reservoir. Also, only about 65 percent of
the water flowing into the reservoir is treated,
adding to the pollution and the possibility of
diseases carried by water.
• The dam sits on a seismic fault, and there is
danger of increased earthquakes and landslides.
Much of the silt that the river used to carry all
the way down to the coast now settles in the
reservoir and reduces the effectiveness of the
dam. Cities such as Shanghai that are far
downstream no longer have silt deposited to help
build up their banks and may soon suffer from
huge erosion problems.
Figure 12.24 The Yangtze River dolphin has become
extinct since the construction of the dam.
• The changes in water flow affect downstream fish
populations. These changes have resulted in the
extinction of the Yangtze River dolphin and may be
harming the populations of critically endangered
Siberian cranes (Figures 12.23 and 12.24).
Analyze and Evaluate
1. Read both students’ viewpoints. Which student
do you think presents a stronger case? Why?
2. Choose one of the following roles. Prepare a
presentation from that perspective, defending a
possible course of action for an international
energy conference.
• relocated villager
• wildlife expert
• government official
• industrialist
• Shanghai citizen
• geologist
• citizen of province receiving electricity from
the dam
Skill Practice
3. What is your conclusion about whether the
electricity the dam provides is worth the
problems it causes? Explain and justify your
conclusion.
Figure 12.23 Siberian cranes
are endangered birds that have
been negatively affected by the
dam’s construction.
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SKILLS YOU WILL USE
D27 Decision-Making Analysis
Skills Reference 4
Producing Electricity in an Ontario Community
Issue
Environmentally, it makes sense to close coalburning generating stations. Open-pit mining of coal
scars the landscape. Burning coal releases pollutants
into the air that cause acid rain. However, it does not
make sense economically for now. The huge amount
of power lost to the grid would have to be replaced.
The job losses would have a devastating effect on
local economies. What recommendations would you
make to a community that relies on burning coal for
electricity generation?
Background Information
Every method of electricity generation has
advantages and disadvantages. For example, the
operation of wind farms along Lake Huron produces
electricity from a renewable source (Figure 12.25).
This reduces dependence on non-renewable sources
of electricity. However, the wind farms produce noise
and visual pollution, affect local animal life, and
reduce the amount of land available for agriculture.
Your goal is to identify some of the social,
economic, and environmental implications of
electricity production in a community in Ontario. You
will research the social, economic, and
environmental effects of one method of electricity
generation that is different from the main method
■
■
Gathering, organizing, and
recording relevant information
from research
Using appropriate formats to
communicate results
being used now in the community. You will also
compare your proposed method to the present
method. Then, you will make a presentation in
support of your choice.
Analyze and Evaluate
1. Meet with your group members to discuss the
role each member will play in researching,
formatting, and presenting your information.
Create a list of questions and key words that will
help direct your research.
2. Web 2.0 Work together to decide on a format for
presenting your research. Develop your group’s
research as a Wiki, a presentation, a video, or a
podcast. For support, go to ScienceSource.
3. ScienceSource Conduct your research online.
Copy and complete the chart below as part of
your research.
Present
Method
Proposed
Method
Economic
- cost of producing electricity
per kW•h
Environmental
- hazardous substances used
or produced and their effects
on surrounding ecosystem
Social
- effects of emissions on
human health
4. What percentage of the energy produced should
come from your proposed method? Explain.
Skill Practice
5. (a) What challenges did you have in researching
the information you needed?
(b) How did you overcome the challenges?
Figure 12.25 Wind farms have to be placed where the wind
is strong and steady enough to generate electricity cost
effectively.
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12.1 CHECK and REFLECT
Key Concept Review
Connect Your Understanding
1. What is the function of a generator?
2. What does “hydroelectricity” mean?
3. What are four methods of generating
electricity that use heat?
4. Explain how a solar cell produces
electricity.
5. What are two different ways to make use of
the tides to generate electricity?
6. (a) What is the difference between
renewable and non-renewable sources
of energy?
(b) Create a chart that categorizes different
energy sources as either renewable or
non-renewable.
7. (a) What is the source of most of the
electricity generated in Ontario?
(b) What is the source of most of the
electricity generated in Canada?
8. The photos below show the type of solar
cells that are installed on the “wings” of the
International Space Station. Why are solar
cells used to generate electricity on
spacecraft?
9. Compare the generation of electricity using
coal with hydroelectric generation.
(a) How are the two methods similar?
(b) How are the two methods different?
10. Why does an electrical generating station
not use batteries to generate electricity?
11. Suppose that residents of a remote
community in northern Ontario decide to
use wood as their primary energy source for
heating the boiler of the community’s
electrical generator. They cut down all the
trees nearby and stockpile the wood, ready
for use.
(a) What are the advantages and
disadvantages of their solution for their
energy needs?
(b) What recommendations would you
make to ensure that this community has
a reliable long-term energy supply?
Reflection
12. (a) What information about electricity
generation did you learn in this section
that you did not know before?
(b) What are two questions that you have
about electricity generation in Canada?
For more questions, go to ScienceSource.
(a)
Question 8
(b)
The International Space Station (a) uses
2500 m2 of solar cells (b) to generate its
electricity.
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Reducing Our Electrical Energy Consumption
Here is a summary of what you
will learn in this section:
• Electrical energy consumption
is usually measured in kilowatthours (kW•h).
• Efficiency is the ratio of useful
energy that comes out of a
device to the total energy that
went in.
• The EnerGuide label shows
how much energy an appliance
will use in a month of average
use.
• Energy Star appliances are the
most efficient appliances in
their class.
• Energy conservation begins at
home.
Figure 12.26 Consider how many times a day and how many different ways you use electricity.
The Cost of Electricity
Every method of generating electricity comes at a cost. There is
an environmental cost, which affects the world you live in, and
there is an economic cost, which gets passed on to you, the
consumer. Each time you plug in an appliance, turn on a switch,
or use electricity in any way, you are using precious resources and
spending money (Figure 12.26). You can take steps to make better
choices about how you use electricity. The first step is to
understand where, when, and how you use electricity.
Most homes and apartment buildings
have an electricity meter that tracks how
much electricity is drawn from the energy
grid. Older models of electricity meters
have a turning disk with a black band
(Figure 12.27). The more electricity you
have turned on in the house, the faster the
disk turns. The energy used is calculated
monthly or bi-monthly by reading a set of
dials above the disk.
Figure 12.27 Older-style meters have to be read manually.
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Newer digital meters, called smart meters, are
being installed across Ontario as part of a major
energy conservation effort. The smart meters
record electricity consumption hour by hour and
send the information directly to the utility or
electric company (Figure 12.28). Electricity costs
are then calculated according to time of use, which
includes time of day, weekdays versus weekends,
and season.
The cost of electricity is higher during peak
times, which are the busiest times of the day. You
can save money on your electricity bill by moving
activities that are energy-intensive to off-peak
hours. You can help save resources by reducing
your use of electricity at all times of the day.
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Figure 12.28 Smart meters use wireless and other
technologies to send information directly to the utility.
D28 Quick Lab
Analyzing Home Electrical Use
Purpose
Clock radio
Dishwasher
Number of devices
3
1
Time of day
all
all
1. Create a list of all devices in your home that use
electricity provided by the electric company or a
home generator. Do not include anything powered
by batteries, but do include battery chargers.
Day(s) of week
all
all
Season
all
all
2. Make a table using the rows shown on the right
but without including the example devices. Add
enough columns for all the electrical devices in
your home. Give your table a title.
Weekly usage (h)
per device
168
7
Total weekly usage
of devices (h)
504
7
3. Complete the table by estimating average usage
and predicting the electricity requirements.
Electricity
requirements per
use (low, medium,
high)
low
high
To categorize the use of electrical devices in your
home
Procedure
Questions
4. Which device usages do you think you could
reduce?
5. What did this activity show you about your
electricity usage that you did not realize before?
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Electrical Energy Consumption
The electrical energy consumption for a
household is the amount of electrical energy
used, usually measured in kilowatt-hours. A
kilowatt-hour (kW•h) is equivalent to the
use of one kilowatt in one hour. For example, if
the energy (E) used by a microwave oven is
0.8 kW and the oven is turned on for half an
hour, the electrical energy used is:
E = 0.8 kW × 0.5 h
= 0.4 kW•h
Figure 12.29 A utility bill shows the amount of electricity used
in kilowatt-hours.
W O R D S M AT T E R
The watt is named in honour of the
Scottish inventor and engineer James
Watt (1736–1819), whose
improvements to the steam engine
changed the world. The joule is
named in honour of English physicist
James Prescott Joule (1818–1889),
who studied the nature of heat and
current through a resistor.
One kilowatt (kW) equals 1000 watts (W).
A watt is equal to one joule per second. It does
not take long for common electrical devices to
consume a large number of joules. For this
reason, the kilowatt-hour is often used as a
unit for energy.
To calculate the cost of using an electrical
device, you can multiply the energy consumed
in kW•h by the cost per kW•h. In the
microwave example above, the consumption of
0.4 kW•h at a cost of 8 cents per kW•h equals
3.2 cents. It may not sound like much, but
remember that this was only one event over a
half-hour time period. There is also an
electricity delivery charge and taxes on top of
the actual energy charge (Figure 12.29).
Learning Checkpoint
1. Copy and complete this chart in your notebook. Give your chart a title.
Calculate the cost of using each appliance over the course of a year. Use a
utility charge of 8.5 cents per kW•h.
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Annual Energy
Consumption
(kW•h)
Appliance
Average Use
(hours per day)
Vacuum cleaner
0.1
38
Hair dryer
0.25
100
Computer
4.0
520
Central air conditioning
12 (60 days/year)
1500
Annual Cost
($ per year)
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Calculating Percent Efficiency
During Writing
If you have ever accidentally touched a light bulb when it was lit,
you know that it gets very hot (Figure 12.30). An incandescent light
bulb uses only about 5 percent of its input energy to create light and
converts over 95 percent of its input energy into heat. Compact
fluorescent lights transform about 20 percent of their energy input
into light, so they are more efficient than incandescent light bulbs.
Organize for Impact
5 J light energy
95 J heat
100 J electric energy
Figure 12.30 Most of the energy
transformed by a light bulb is
radiated as heat.
The efficiency of a device is the ratio of the useful energy that
comes out of the device to the total energy that went in. The more
input energy that a device converts into usable output energy, the
more efficient the device is. Efficiency is usually calculated as a
percentage.
percent efficiency =
Suggested Activities •
D30 Quick Lab on page 496
D31 Quick Lab on page 497
Eout
× 100%
Ein
Example Problem 12.1
Suppose a light bulb uses 780 J of input energy to produce 31 J
of light energy. What is its percent efficiency?
Given
Input energy = 780 J
Output energy = 31 J
Required
Percent efficiency = ?
Analysis and Solution
Choose the correct equation.
Percent efficiency = Eout × 100%
Ein
Substitute the values and their units. Solve the problem.
Percent efficiency = 31 J × 100%
Paraphrase
When persuasion is the goal,
good writers like to create impact
at the beginning and end of their
piece of writing or presentation.
Watch television commercials,
especially public service
announcements, and note the
methods for creating a powerful
opener and a convincing closer
for your presentation.
780 J
% = 4.0%
The efficiency of the light bulb is 4.0 percent.
Practice Problems
1. A car produces 27.5 kJ of
useful output energy from
125 kJ of fuel. What is
the car’s percent
efficiency?
2. A fluorescent light
produces 3.6 kJ of useful
light energy from 21 kJ of
input energy. What is its
percent efficiency?
3. A new high-efficiency
brushless motor designed
for electric-powered
vehicles has an input
energy of 75 kJ and an
output energy of 72 kJ.
What is its percent
efficiency?
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Comparing Efficiency
By comparing the efficiency of different devices, we can judge
both their energy cost and their environmental impact. For
example, a front-loading clothes washing machine uses much less
electricity, washes more clothes per load, and uses less water than
a top-loading washer. This reduces the energy needed to pump
and heat water for laundry. Another example of improved
efficiency is the refrigerator shown in Figure 12.31.
thin
fiberglass
insulation
thick
polystyrene
insulation
low-efficiency
compressor
motor
high-efficiency
compressor
motor
1970s mini-refrigerator
Modern full-size refrigerator
Figure 12.31 The energy used to run a mini-refrigerator in the 1970s can run a full-size
refrigerator today. In the last 25 years, refrigerator efficiency has increased 300 percent.
Read the Label
Sometimes, older equipment can be modified or adjusted
to increase efficiency. But when it is time to buy a new
appliance, there are labels that can help you make an
informed choice.
All large appliances such as stoves, dishwashers,
refrigerators, washers, and dryers have an EnerGuide
label. This label states how much energy that appliance
will use in a month or year of average use, as shown at
(a) in Figure 12.32. It allows you to compare the energy
consumption of different brands and models. The arrow
(b) on the long shaded bar on the label below the rating
shows the efficiency range of the appliance. If an
appliance displays the Energy Star symbol (c), it is one
of the most efficient appliances in its class.
(a)
(b)
(c)
Figure 12.32 You can use the EnerGuide label to compare appliances and
determine which are more efficient. For example, you could compare refrigerators
that have the same volume but are made by different manufacturers.
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How Off Is Off?
Suppose you finish using your computer and turn it off before
leaving your room. As you walk by the living room, you notice
the television has been left on even though no one is watching it,
so you turn it off as well. These are good, energy-conserving
actions, but have you really turned those appliances off?
If you look more closely, you may notice little lights still
glowing on transformers and other devices (Figure 12.33). These
machines are in a “standby” mode so that they will restart quickly
when you switch them on. Many small appliances, such as
computers, stereos, televisions, DVD players, and answering
machines, still use electrical energy even when they are
turned off.
Figure 12.33 If the standby light is
on, electricity is being consumed.
Energy Conservation Begins at Home
You can make a plan to reduce the use of electricity in your home.
Asking questions is an excellent start. For example:
• Are lights being left on in rooms that are not being used?
• Is the clothes dryer being used for small loads like one shirt?
• Is the hot water running continuously while the dishes are
being done?
• Is a lot of hot water being used for long showers?
• Are incandescent light bulbs being used instead of compact
fluorescent bulbs?
If we lower our energy demands, we reduce the need to build
more generating stations and we avoid greater impact on the
environment and major construction costs. Your own personal
action plan to reduce energy consumption will make a difference.
Reusing and recycling materials, conserving energy, and learning
to live responsibly in harmony with our environment are key
actions for living in a sustainable way.
Take It Further
Many people have contributed to
our understanding of electricity.
Research one of the following
names to find out when these
people lived and what they
contributed: Benjamin Franklin,
Luigi Galvani, Charles-Augustin de
Coulomb, Alessandro Volta, James
Watt, André-Marie Ampère, Georg
Ohm, Robert Millikan, Michael
Faraday, Thomas Edison, Nikola
Tesla, George Westinghouse. Begin
your research at ScienceSource.
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STSE Science, Technology, Society, and the Environment
A Self-Sufficient Energy Community
The 4300 people of Freiamt, a community in the
southern part of Germany, decided that they
wanted to own and control their own electricity
generation. The community added rooftop solar
systems to homes, barns, and garages and
installed wind turbines. The community also has
small-scale hydro and biomass generating
stations. Some of the generators are jointly
owned; others are privately owned.
The community’s electricity generation has
been so successful that each year there is a surplus
of about three million kilowatt hours of energy that
is sold to Germany’s national energy grid.
1. How could you adapt the community’s plan
to make it suit your community?
2. What do you think are the main points about
Freiamt’s plan that you could use to gain
community support?
D30 Quick Lab
Electricity in Your Home
Purpose
To discover the pattern of electrical energy
consumption in your home
Materials & Equipment
• 1 year’s worth of electrical bills for your home or
sample bills supplied by your teacher
Procedure
1. Before starting, predict what months are the
peak periods of electrical energy consumption in
your home.
2. Create a table with the following column
headings. Give your table a title.
Actual Electricity Usage (kW•h)
Adjusted Usage (kW•h)
Cost of Electricity ($)
Delivery Charge ($)
Other Charges ($)
Total Charges
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3. For each bill, break down the different costs and
add them to your chart.
4. Total the charges.
Questions
5. (a) What does the category “Other Charges ($)”
include?
(b) What does “Adjusted Usage (kW•h)” mean?
6. (a) During which time periods is your household
using electricity the most?
(b) Why might this be?
(c) How does this time period compare with your
prediction from step 1?
7. How would you change the bill to make it easier
to understand?
8. Write a summary paragraph explaining the
pattern of electricity usage in your household.
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DI Key Activity
D31 Quick Lab
Marketing Compact Fluorescent Light Bulbs
As part of an effort to reduce energy use, the
province of Ontario has banned the sale of inefficient
incandescent bulbs, beginning in 2012.
Purpose
To create an effective marketing tool for compact
fluorescent light bulbs
Procedure
1. You and your partner have been hired by a
public relations firm to help with the marketing
campaign for compact fluorescent light bulbs
(Figure 12.34).
2. Decide on the format you will use as part of the
marketing campaign. You might design a
brochure, make a poster, create a Web page,
prepare computer slides, perform a rap song,
create a skit, or choose another format as
approved by your teacher.
3. Read the following summary of points about
both incandescent and compact fluorescent light
bulbs. Consider both the pros and the cons in
deciding how to reach your audience.
Bulb
Pros
Cons
Compact
fluorescent
- produces about
four times more
light than
incandescent
using the same
amount of
energy
- much more
expensive to
make than
incandescent
- contains
mercury
Incandescent
- less expensive
to make than
fluorescent
- does not last
as long as
fluorescent
- is much less
efficient than
compact
fluorescent
bulbs
4. ScienceSource Conduct research so you can
make a strong case in favour of compact
fluorescent light bulbs. You may want to
research Ontario Power Generation, the Ontario
Ministry of the Environment, Natural Resources
Canada, and environmental groups such as the
Pembina Institute or the Sierra Club.
5. Outline the roles and responsibilities of various
groups, such as government, businesses, and
family members, in making a success of the
marketing campaign.
6. Look in print materials such as magazines,
newspapers, and books for information on the
real costs of using various lighting options.
7. Prepare and refine your presentation. You may
wish to present your information to friends or
family members and ask for their feedback.
8. Share your presentation with the class.
Questions
9. On the basis of your research, what do you think
is the most important advantage of compact
fluorescent bulbs?
10. On the basis of your research, what do you think
is the greatest disadvantage of compact
fluorescent light bulbs?
Figure 12.34 Compact fluorescent bulbs (left) are replacing
incandescent bulbs (right) because they use less energy.
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12.2 CHECK and REFLECT
Key Concept Review
10. What does an Energy Star symbol on an
appliance indicate?
1. What does a smart meter measure?
2. (a) What is electrical energy consumption a
measure of?
(b) What units are usually used to measure
electrical energy consumption?
(c) How is electrical energy consumption
calculated?
Question 10
3. (a) How many watts are in a kilowatt?
(b) What does one thousand joules equal?
4. (a) A microwave oven that draws 0.8 kW•h
is used for one hour. At a cost of
7.5 cents per kW•h, what is the cost of
the microwave’s electrical energy
consumption?
(b) What is the cost for the microwave if it
is used one day for 20 min?
(c) What is the cost of using the microwave
for 20 min a day for a month of 30
days?
5. What is the term for the ratio of useful
energy that comes out of a device to the
total energy that went in?
6. What is the formula for calculating percent
efficiency?
7. What is the percent efficiency of a light
source that uses 12.8 kJ of energy and
delivers 4.3 kJ of useful light energy?
8. What information is included on an
EnerGuide label?
9. Suppose the standby light on your printer is
on even though you have turned the printer
off. What does the standby light indicate?
Connect Your Understanding
11. Describe how a smart meter is an
improvement over older types of electricity
meters.
12. The costs for electricity are higher during
peak times. Why do you think this is so?
13. Why are incandescent bulbs regarded as
inefficient?
14. Create an EnerGuide label for an appliance
with an Energy Star rating. You can use
hypothetical values and names of
companies.
15. Why should you compare the efficiencies of
appliances before making a purchase?
16. How can we reduce the need to build more
generating stations?
Reflection
17. (a) How has the information in this section
helped to make you a better consumer?
(b) How could you use this information to
help you decide which electronic device
to purchase?
For more questions, go to ScienceSource.
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COOL IDEAS
f r o m J AY I N G R A M
A Light Show in Your Mouth
Jay Ingram is an experienced
science journalist, author of The
Daily Planet Book of Cool Ideas,
and host of the Daily Planet on
Discovery Channel Canada.
Have you ever experienced a chemical light show in your mouth? You
might have if you have chewed a wintergreen candy.
You can observe the effect if you get some wintergreen candies and a
pair of pliers, and sit in a very dark place, like the inside of a closet. Wait
about five minutes until your eyes adjust to the darkness, and then crush
one of the candies with the pliers (Figure 12.35). You will see an
amazing flash of blue-green light!
The flash of blue-green light was first described in 17th century
Italy. However, the mechanism at work was not understood
until several hundred years later.
The candy is made of sugar crystals, which are
mostly empty space, with the atoms in them rigidly
attached to each other. When you bite into the
candy, the positive and negative charges in the
crystals are separated, and this separation
generates an electric potential difference.
When enough charge has accumulated,
the negatively charged electrons jump
across the gaps in the crystals to reunite
with the positively charged protons.
As the electrons move, some of them
collide with the nitrogen atoms in the air.
The nitrogen atoms absorb the
tremendous energy of the collisions, and
then emit blue-green light as they release
their energy.
All sugar candy emits some light when
you crush it. If there is only sugar, the blue
light is harder to see, because much of the
energy is released as ultraviolet light, which is
not visible to humans. That is where the
wintergreen comes in. Oil of wintergreen is very good
at absorbing ultraviolet light and emitting it as visible
blue-green light.
Question
1. Write a summary of this feature. Include a main idea and one
relevant point that supports it.
Figure 12.35 A wintergreen candy
crushed by pliers in the dark.
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12 CHAPTER REVIEW
ACHIEVEMENT CHART CATEGORIES
t Thinking and investigation
k Knowledge and understanding
c Communication
9. How can choosing to use a more efficient
appliance benefit the environment? k
a Application
10. Answer the following questions by
referring to the EnerGuide label shown
below. k
Key Concept Review
1. (a) List two non-renewable sources of
energy. k
(b) Name an advantage and a disadvantage
of using each source. k
2. (a) List four renewable sources of energy.
k
(b) Name an advantage and a disadvantage
of using each source. k
3. Describe what happens in nuclear
fission. k
4. What is sustainability?
k
5. (a) How do you convert watts to kilowatts?
k
(b) How do you convert kilojoules to
joules? k
(c) How many joules are in a watt?
Question 10
k
6. Suppose you bake a potato in a toaster oven
that uses 1.2 kW. The oven is turned on for
25 min. How many kilowatt hours did it
use? a
7. (a) If a motor uses 22 000 J while
converting it to 13 400 J of useful
energy, what is its percent efficiency?
(b) If a diesel truck produces 47.5 kJ of
useful output energy from 125 kJ of
diesel fuel, what is its percent
efficiency? a
8. Give two reasons for reducing energy
waste. k
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a
(a) What is the energy usage of the rated
appliance?
(b) Among similar appliances, which is
rated most efficient?
(c) Is the rated appliance efficient? How do
you know?
(d) List models similar to the one that is
being rated.
11. What does it mean if an appliance has an
Energy Star rating? k
Connect Your Understanding
12. Explain why you agree or disagree with the
following statement: “A nuclear power
plant provides energy using a radioactive
source, so a turbine is not needed.” t
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13. A group of Ontario farmers form a
cooperative group and build a factory that
turns corn into a fuel for generators and
cars. Would this energy source be renewable
or non-renewable? Explain. t
14. Make a labelled pie chart or circle graph
showing how electricity is used in your
home. c
15. Is it always a good idea to discard lowefficiency devices? Explain your answer.
Question 20
t
16. (a) If you have a house in the country with
a large property, what might you do to
help reduce your dependence on the
energy grid? t
(b) If you live in a mid-size house in the
suburbs, what could you do to reduce
your utility bill? t
(c) If you live in a small apartment in the
centre of a city, what could you do to
reduce your utility bill? t
17. Choose an electrical device that you use
daily. Identify changes you would make to
the design of the device to maximize energy
savings. Explain the reasons for your
choices. Use a labelled diagram as part of
your answer. c
18. (a) Create a cartoon that shows at least
seven ways that a home loses energy
needlessly. c
(b) For each example shown, list a way to
reduce that energy loss. t
19. What are seven practical ways to reduce
electrical energy consumption in your
school? t
20. Write a paragraph about the photograph
shown at the top of the next column.
Include your personal response to the
photograph, and explain what the
photograph shows about electricity
generation. c
Reflection
21. How could you improve the results of your
work in the problem-solving and inquiry
activities you did in this unit? c
After Writing
Reflect and Evaluate
With your partner, meet with another pair who
made a marketing presentation for fluorescent
light bulbs. Provide positive feedback and helpful
suggestions about the others’ presentation. How
did it hook the audience? Which details, facts, or
evidence were most effective in demonstrating
knowledge? What were the points that created the
greatest impact?
Unit Task Link
In this chapter, you have studied different
methods of generating electricity and their social,
economic, and environmental effects. Your
knowledge of electricity can help you work within
your community to decide on the best methods of
power generation for your region. Think about the
sources of energy for your community and
whether they are reliable and sustainable. Suggest
one form of energy production not being used
now that might be an appropriate method for your
community. Explain your choice.
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UNIT
Summary
KEY CONCEPTS
10
CHAPTER SUMMARY
Static charges accumulate on surfaces and remain there until given a path to escape.
• Static electric charges
• Law of attraction and law of
repulsion
• Conductors and insulators
• Charging by friction
• Charging by contact and
induction
• Using and reducing static charges
• Objects that gain electrons become negatively charged. Objects that lose electrons
become positively charged. (10.1)
• Objects with like charges repel each other. Objects with unlike charges attract
each other. (10.1)
• When an object is charged by contact, it takes the same charge as the charging
object. (10.2)
• When an object is charged by induction, it takes the opposite charge to the
charging object. (10.2)
• Charged objects attract neutral objects through the process of induction. (10.2)
• The principles of electrostatics are used in applications such as photocopying,
spray painting, and filtering air. (10.3)
11
Current electricity is the continuous flow of electrons in a closed circuit.
• Current electricity
• Electrical circuits provide a complete path for electrons to flow. (11.1)
• Electrical circuits
• Current electricity is the flow of electrons through a conductor in a circuit. (11.1)
• Potential difference
• Electric current
• Direct current
• Alternating current
• Resistance
• Series circuits and parallel
circuits
• Ohm’s law (V = IR)
• Electrical safety
• Potential difference or voltage (V ) is the difference in electric potential energy
between two points in a circuit. (11.1)
• Electric current (I ) is a measure of the amount of electric charge that passes by a
point in an electric circuit each second. (11.1)
• In direct current, electrons flow in one direction. In alternating current, electrons
flow back and forth at regular intervals called cycles. (11.1)
• Resistance (R ) is the degree to which a substance opposes the flow of electric
current through it. (11.1)
• Series circuits provide one path for electrons to flow. Parallel circuits provide more
than one path for electrons to flow. (11.2)
• Ohm’s law states that as long as temperature stays the same, V = IR. (11.3)
12
We can reduce our electrical energy consumption and use renewable energy resources.
• Generating electricity
• Renewable and non-renewable
sources of energy
• Advantages and disadvantages of
energy sources
E
• Percent efficiency = out × 100%
Ein
• Non-renewable sources used for generating electricity include fossil fuels and
nuclear energy. (12.1)
• Renewable sources used for generating electricity include water, sunlight, wind,
tides, and geothermal energy. (12.1)
• There are both costs and benefits from producing electricity from renewable and
non-renewable sources. (12.2)
• Electrical savings can be achieved through the design of technological devices
and practices in the home. (12.2)
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The Characteristics of Electricity
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VOCABULARY
• charging by contact
(p. 407)
• conduction (p. 400)
• conductivity (p. 400)
• conductor (p. 400)
• coulomb (C) (p. 399)
• electric charge
(p. 394)
• electrical discharge
(p. 411)
KEY VISUALS
• electron (p. 396)
• electron affinity
(p. 398)
• electroscope (p. 404)
• electrostatics (p. 404)
• friction (p. 399)
• grounding (p. 408)
• induction (p. 407)
• insulator (p. 400)
• law of attraction
(p. 399)
• law of repulsion
(p. 399)
• lightning rod (p. 418)
• neutron (p. 396)
• nucleus (p. 396)
• proton (p. 396)
• static charge (p. 396)
• static electricity
(p. 396)
• alternating current
(AC) (p. 439)
• electric current (l )
(p. 439)
• potential difference
(p. 437)
• ammeter (p. 439)
• ampere (A) (p. 439)
• electrochemical cell,
(p. 435)
• potential energy
(p. 437)
• battery (p. 435)
• electrode (p. 435)
• resistance (R) (p. 441)
• circuit breaker (p. 463)
• electrolyte (p. 435)
• resistor (p. 441)
• circuit diagram (p. 450)
• fuel cell (p. 486)
• series circuit (p. 451)
• current electricity
(p. 434)
• fuse (p. 463)
• short circuit (p. 462)
• ground fault circuit
interrupter (p. 464)
• switch (p. 434)
• ohm (Ω) (p. 441)
• volt (V) (p. 438)
• direct current (DC)
(p. 439)
Lightning strike
• transistor (p. 449)
• dry cell (p. 435)
• ohmmeter (p. 441)
• voltage (V ) (p. 437)
• electrical circuit
(p. 434)
• Ohm’s law (p. 463)
• voltmeter (p. 438)
• parallel circuit (p. 451)
• wet cell (p. 435)
• electrical load (p. 434)
Microcircuits
• biomass (p. 478)
• efficiency (p. 493)
• EnerGuide (p. 494)
• energy grid (p. 476)
• Energy Star (p. 494)
• fossil fuels (p. 478)
• generators (p. 476)
• geothermal energy,
(p. 479)
• renewable energy
sources (p. 474)
• hydroelectricity
(p. 477)
• thermoelectric
generating plant
(p. 478)
• kilowatt-hour (kW•h)
(p. 492)
• non-renewable energy
sources (p. 474)
• thermonuclear (p. 470)
• turbine (p. 476)
Solar panels on rooftop
UNIT D
Summary
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UNIT
Task
Bringing Electrical Energy to a Community
Criteria for Success
• Your plans for generating electricity must be
environmentally responsible. For example, a
plan to build a new dam across a river will need
to consider the effect of creating a new lake, as
well as the effect on migrating species of fish.
• Your plans for power generation must align with
the other groups so that two groups are not
competing to use the same natural resource,
such as having two dams very close together.
Solar cells can be used to generate electricity for individual
buildings.
Getting Started
You are an electrical energy consultant working on a
plan to add additional electrical energy generating
sources in an area prone to blackouts. Suppose your
electricity has a main supply source, such as a coal
power plant or a nuclear power plant. However, a
number of environmental factors have led to frequent
blackouts. These factors include high winds and icing
problems with transmission lines.
Your job includes developing new, smaller electricity
generation sources. Each of these sources can connect
to the regional electrical grid when the main source goes
off-line or when main transmission lines to the grid fail.
These new, smaller-scale sources will help provide a
consistent supply of electrical energy to the region, even
if the main electrical supply becomes unavailable.
• The types of generating methods your groups
research must not all be the same. For
example, if all groups plan a solar power
generating station, this will be of little use if a
blackout occurred at night.
• Your plans must be supported by references to
existing examples of electrical generation
sources. You will need to research your example
enough to know what will be necessary to adapt
it to your particular location. For example, if an
oil-fired generating source is needed, will you be
able to use a technology that captures and stores
carbon dioxide emissions?
• Each group will submit a plan in order to create
a class report that solves the problem of using
backup generators to maintain consistent
production of energy to the electrical grid.
Your Goal
Your group will be in charge of planning a backup
electrical generating station by researching existing
examples of generating stations or technologies that can
be used to generate electricity. Low-cost and
environmentally friendly technologies are preferred. As a
class, you will be required to propose a wide variety of
technologies.
Wind turbines can be used individually for small-scale
electricity generation. They can also be grouped in wind farms
for larger-scale generation.
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The Characteristics of Electricity
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What You Need to Know
A century ago, energy was generated in the same
location that it was used or only a few kilometres away.
Over the past 100 years, extensive electrical grids have
been developed that are powered mainly by large
generating stations. In many cases, smaller generating
stations were discouraged or even prohibited from
adding energy to the electrical grid.
This is beginning to change as many smaller, more
efficient, and often more environmentally friendly ways
of generating power are being encouraged.
For this task, you need to research one or more of
these newer technologies for generating electricity by
finding existing examples of where they are being used.
You will then determine ways to adapt them to your local
region.
What You Need
• a large map of your region showing population centres,
useful geographical features, and main lines of the
power grid
• Internet access for researching examples of methods of
electrical power generation
Procedure
1. As a class, decide on the number of new generating
stations that can be planned. Do this by dividing the
size of the class by the size of each planning group.
2. As a class, brainstorm the specific geographical
features that may be of use for electrical power
generation in your community. This may involve
using only real features in your area, or you may
agree to include features not actually present but
which will be useful for the purpose of this activity.
Examples of features could include a fast-flowing
river or waterfall, a high ridge that is usually windy, a
large water supply useful for construction of cooling
towers, or geothermal energy. You may wish to
estimate the average annual hours of sunshine to
determine whether to include solar energy.
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3. Form groups, and within your group brainstorm
ideas for electrical generation methods. Agree on
several options to bring back to the class for
discussion.
4. As a class, share the ideas of each group.
Remember that methods of electrical generation
must be varied and must not conflict with each
other or represent a threat to the environment.
Agree as a class on what type of power generating
source each group will investigate and where on the
regional map each generating station will be located.
5. ScienceSource Research a plan for your generating
station by examining existing stations or
technologies already.
6. Design your generating station. Use clearly labelled
diagrams.
7. Present your plan for the generating station.
Describe how it fits into the overall regional plan with
all of the groups’ plans.
Assessing Your Work
8. (a) Think about your role in the work your group
accomplished. What do you think was the
strongest contribution you made to your group’s
work?
(b) How could you improve your contribution to
group work in future activities?
9. (a) What do you feel was the most effective aspect
of your group’s plan?
(b) How could your group’s design have been
improved?
10. Write an evaluation of your approach to solving this
problem. Did it work well? What would you have
done differently and why?
UNIT D
Task
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UNIT
Review
ACHIEVEMENT CHART CATEGORIES
k Knowledge and understanding
t Thinking and investigation
c Communication
a Application
7. Suppose you know that balloon A below is
negatively charged but you do not know the
charge on balloon B.
Key Terms Review
1. Create a mind map using the following
terms. You may add more terms if you
wish. c
• ammeter
• ampere
• battery
• current
• fuse
• kilowatt-hour
• load
10
• ohm
• potential difference
• resistance
• switch
• voltmeter
• volt
Static charges accumulate on surfaces
and remain there until given a path to
escape.
2. (a) Suppose you walk across the carpet,
touch a metal doorknob, and get a shock.
What charge do the particles causing the
charge have: negative or positive? t
(b) Use the structure of the atom to explain
why these particles have the charge you
identified in part (a). k
3. (a) State the law of attraction.
k
(b) State the law of repulsion.
k
4. Explain the steps you would take to tell the
difference between a positively charged
object and a negatively charged object. k
5. Use a series of diagrams to explain how a
charged object attracts a neutral object. c
6. Suppose two different materials are rubbed
together. Each one is brought near a
charged electroscope with no effect on the
electroscope. Explain what may be the
reason that there is no effect. k
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+
–
–
–
+
–
?
–
A
B
Question 7
(a) When you bring the two balloons
together, they repel each other. What is
the charge on balloon B? k
(b) Suppose that when you bring the two
balloons together they attract each
other. Does this observation prove that
balloon B is positive? Explain why or
why not. k
8. Object C is rubbed on object D. The leaves
of a negatively charged electroscope
temporarily move closer together when
object D is brought near.
(a) What charge does object D have?
k
(b) What charge does object C have?
k
9. Use a Venn diagram to compare and
contrast charging by contact and charging
by induction. k
10. Use labelled diagrams to explain how
lightning occurs. c
11. (a) When clothes come out of a clothes
dryer, they sometimes stick to each
other. Explain why. k
(b) Name three different ways to reduce
this effect. k
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12. Explain the function of the metal rods in
the photograph below. k
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18. Why does a light bulb light up immediately
after you turn on a switch, even if the
switch is a long way from the bulb? k
19. (a) Draw a circuit diagram that includes a
battery, connecting wires, and a resistor.
a
(b) Add a voltmeter to the circuit diagram
to measure the potential difference
across the resistor. a
Question 12
13. How have static electricity controls helped
in developing new technologies? k
14. (a) Name one device that would function
better if static electricity were
eliminated. k
(b) Name one device that would not
function as well if static electricity were
eliminated. k
11
Current electricity is the continuous flow
of electrons in a closed circuit.
15. (a) What are the two main components of
an electrochemical cell? k
(b) What is the function of each
component? k
16. Copy and complete the following chart in
your notebook. k
Definition
Abbreviation
Unit
Potential
difference
a
20. (a) Use circuit symbols to draw a series
circuit with a battery, connecting wires,
and two light bulbs. a
(b) Draw a parallel circuit using the same
components as (a). a
(c) Describe the difference in current
flowing in the two circuits (a) and (b).
a
(d) What will happen to the brightness of
the bulbs in circuit (a) if one of the
bulbs is unscrewed? a
(e) What will happen to the brightness of
the bulbs in circuit (b) if one of the light
bulbs is unscrewed? a
21. (a) What is the voltage at V1 in the circuit
below? a
(b) What is the current at A1 in the circuit
below? a
Potential Difference, Current, and Resistance
Quantity
(c) Add an ammeter to the circuit diagram
to measure current through the resistor.
Symbol
(c) Is this circuit a series circuit or a
parallel circuit? k
Current
2.0 A
Resistance
V1
9.0 V
17. (a) What are four factors affecting
resistance in a wire? k
(b) Describe how each factor affects
resistance. k
3.0 V
A1
Question 21
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UNIT
Review
(continued)
22. (a) What is the voltage at V1 in the circuit
below? a
(b) What is the current at A1 in the circuit
below? a
(c) Is this circuit a series circuit or a
parallel circuit? k
V1
30. What are three different electricity
generating systems you could use on your
property to provide electrical energy if you
lived on a small farm? k
31. What effects do the following electricity
generation methods have on surrounding
ecosystems?
3.0 A
2.0 A
29. How is steam used in the generation of
electricity? k
A1
(a) wind farms
3.0 V
k
(b) hydroelectric dams
Question 22
23. Draw a circuit that keeps two lights on at
all times and can switch two other light
bulbs on and off independently. a
24. What does Ohm’s law state?
k
25. If the resistance of a load becomes larger,
does current also become larger? Explain
your answer. k
26. Most homes in Ontario are built to meet
regulations that ensure safety and
dependability of electrical systems. What
are some ways in which the electrical
system in your home has been made as safe
as possible? k
k
32. What types of hazardous substances are
used or created in the production of nuclear
power? k
33. State some disadvantages of:
(a) solar power
k
(b) tidal power
k
34. What is the price difference between
electricity produced from solar power and
by coal-burning plants? k
35. In what units is electrical energy
consumption usually measured? k
36. The efficiency of a device is a ratio. What is
it a ratio of? k
27. Why is it a good idea to use fused safety
power bars for televisions, computers, and
other sensitive electrical equipment? k
37. What information does an EnerGuide label
provide? k
We can reduce our electrical energy
consumption and use renewable energy
resources to produce electrical energy.
39. How could you use the EnerGuide and
Energy Star labels to help you decide when
purchasing appliances or electronics? k
12
28. (a) Describe the difference between
renewable and non-renewable energy
sources. k
(b) Give two examples of each type of
source. k
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38. What does an Energy Star label indicate?
k
40. What causes the difference in energy
consumption between a conventional and a
front-loading washing machine? k
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41. List five appliances found in the home that
consume electrical energy even when they
are not in use? k
47. How does the charge on a charged
electroscope compare with the charge in a
functioning circuit? t
42. What are three benefits of lowering our
energy demands? k
48. Explain why a cow that touches an electric
fence gets a mild shock. A bird sitting on
the same wire does not receive a shock.
Why? a
Connect Your Understanding
43. (a) When lightning hits a car, is it safer to
be in the car or outside the car but
touching it? Explain why. a
(b) You are standing close to a tall tree when
you suddenly see lightning and hear
thunder. Should you take shelter under
the tree, run across the field to the
nearest building, or do something else?
Explain why. a
44. How are a lightning bolt and a spark
similar? t
45. You have just combed your hair, and you
bring the comb near some bits of paper. The
paper is attracted to the comb, but as soon
as the paper touches the comb, it is
immediately deflected away. Explain what
is happening in terms of charge motion,
charging methods, and the triboelectric
series. t
46. Some machines have a
grounding screw
connected to a wire or
cable as shown in this
photograph.
(a) Explain what
grounding a charged
object does. k
49. The voltmeter and the ammeter are
electrical loads. Each has an internal
resistance. Relative to the resistors in the
circuit, would their internal resistances be
large or small? Explain. t
50. Why do lights dim in the house when
certain appliances, such as an oven, hair
dryer, or table saw, are used? t
51. For the following situations, explain the
safety concern. a
(a) A worker carries a large aluminum
ladder near overhead hydro lines.
(b) Someone takes the third prong out of a
plug in order to use it with a two-prong
extension cord.
(c) The washing machine electrical cord is
frayed.
(d) You run out of fuses and put a piece of
aluminum in place of the fuse.
52. A friend replaces a cord on a kettle with a
new cord that is much thinner than the
original. When the kettle is plugged in, the
new cord gets much hotter than the old one
did. Explain why. t
Question 46
(b) Explain why some objects need to be
grounded. k
(c) Give two examples of machines or
devices that need to be grounded. t
53. Could a thermal generating plant be
effective without a turbine? Explain.
t
54. (a) What is meant by a “non-thermal”
method of generating electricity? t
(b) Describe an example of such a
method. t
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(continued)
55. Suppose a more efficient appliance costs
more than a regular appliance. Does it make
sense to spend the extra money? Explain. t
56. Create a sketch, paragraph, or skit using
electrical terms in a humorous manner. You
should get a “charge” from doing this
“potentially” fun exercise at “ohm” or at
school. c
61. The graph below shows the relationship
between voltage and current that emerged
in tests for a particular resistor. Does this
resistor work according to Ohm’s law?
Explain. t
Current vs. Voltage
Skills Practice
c u rre n t
57. What is the value of a resistor that
transforms 2.0 mA of current when it is
connected to a 6.0-V battery? a
v o lt a g e
58. (a) What voltage is applied to a 5.0-Ω
resistor if the current is 1.5 A? a
(b) A voltage of 80 V is applied across a
20-Ω resistor. What is the current
through the resistor? a
(c) The current running through a starter
motor in a car is 240 A. If this motor is
connected to a 12-V battery, what is the
resistance of the motor? a
59. Copy and complete
the following chart
in your notebook.
Use Ohm’s law to
create a set of data
given that there are
three resistors in
series and each one
has a resistance of
40 Ω. a
Voltage and Current
Voltage
(V)
Current
(A)
2.0
4.0
(b) 1500 Ω = ____ kΩ
(c) 650 mA = ____ A
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62. Copy and complete the following chart in
your notebook. a
Percent Efficiency
Device
Input
Energy (kJ)
Output
Energy (kJ)
Gaspowered
SUV
675
81
Gas-electric
hybrid car
675
195
Natural gas
furnace
110 000
85 000
Electric
baseboard
heater
9.5
6.0
Alkaline dry
cell
84.52
74.38
6.0
8.0
10.0
60. Copy and convert each of the following
units in your notebook. a
(a) 1.6 MV = ____ V
Question 61
Percent
Efficiency
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Revisit the Big Ideas and Fundamental
Concepts
63. Create a poster on your opinion of one of
the following topics. c
(a) Why we should use renewable sources
to generate electricity
(b) Why we should conserve energy
64. Nuclear energy is one of the most efficient
ways to produce electrical energy. Why are
not all power plants nuclear? a
65. Choose a renewable source for generating
electricity. Explain possible solutions to its
disadvantages. t
66. Create a timeline that begins with this year
and extends 30 years into the future. On the
timeline, detail the steps your community
could take to become energy self-sufficient.
Include: c
•
•
the new technologies for generating
electricity that could be installed,
including where you recommend
installing them
the energy-conserving methods that
could be implemented
67. Write a three-paragraph essay in answer to
the following question: “How can we
improve our lives by controlling, using, and
conserving electricity in an
environmentally friendly way?” c
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STSE
Science, Technology, Society,
and the Environment
68. Create a graphic representation, such as a
mind map or other chart, to answer the
following questions. Include labelled
diagrams if you wish. c
(a) What are the costs and benefits
associated with the production of
electrical energy from renewable and
non-renewable sources?
(b) How can electrical efficiencies and
savings be achieved through the design
of technological devices and practices in
the home?
69. Based on the activities you have done in
this unit, answer the following questions.
Include your personal observations. You
may wish to include labelled diagrams
and/or refer to specific activities as part of
your answer. c
(a) What are the properties of static
electricity and current electricity?
(b) What is the relationship between
potential difference, current, and
resistance in an electrical circuit?
Reflection
70. (a) After completing this unit, how have
you changed your attitude toward how
you use electrical energy? c
(b) What changes are you thinking of
implementing? c
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