Download Section Questions

Hip – Hip – Huzzah!! 
What happened on August 14th, 2003 at 4:11?
1.

50 million people in Ontario and the northeastern US were
plunged into the largest electrical blackout in North American
history.
What were you doing then and how were you affected?
2.

Various answers
What is an “energy grid”?
3.

It is a huge, interconnected system of electricity networks
(which includes electrical generating stations, transmission
lines, and distribution stations).
Why does an energy grid have to balance supply with
the demand for electricity?
4.

It must maintain a balance of supply and demand because
electricity cannot be stored for long after it is generated. If it
isn’t and a generator is overloaded, that part of the energy
grid is disconnected and electricity will be sent along
alternative paths.
A SHOCKING EXPERIENCE
1. What is an electric shock?

It is caused by electric charges that gather or
accumulate, then are released very quickly.
How are lightning and an electric spark
similar?
2.

They are the same thing, just different in size –
they are caused by electric charges, which are
charged particles that exert an electric force
on each other.
ELECTRICALLY CHARGED PARTICLES
1. What is the charge of a proton?

Positive
What is the charge of an electron?
2.

Negative
What is the charge of a neutron?
3.

No charge or neutral
Can an atom lose protons?
4.

No, they are bound to the neutrons in the nucleus.
Can an atom lose electrons?
5.

Yes, they orbit around the outside of the nucleus
and can move from one object to another.
FRICTION AND THE MOVEMENT OF ELECTRONS
1.
What has happened when an object creates a static
charge?
 Electrons have moved from one object to another through
some method, and that electric charge builds up on the
surface of the object.
2.
What is the difference between an object that has a
negative charge and the same object when it has a
positive charge?
 A negatively-charged object has more electrons than
protons, whereas a positively-charged object has more
protons than electrons.
3.
How does rubbing two objects together sometimes result
in the building of a static electric charge?
 The force of friction can remove electrons from one object
and cause them to transfer to the other object.
4.
Where does the word, “electricity” come from?
 It comes from the Greek word electron, meaning amber,
which is fossilized tree resin. It has been used for
thousands of years to study static electricity.
ELECTRON AFFINITY
1.
What does “electron affinity” mean?
 It is the tendency of a substance to hold on to the electrons.
2.
If you rub nylon and steel together which one becomes negative and why?
 Steel becomes negative because steel is lower on the triboelectric series.
3.
If you rub amber and silk together which one becomes negative and why?
 Amber becomes negative because amber is lower on the triboelectric
series.
4.
If you rub Teflon and human hair together which one becomes negative and
why?
 Teflon becomes negative because Teflon is lower on the triboelectric
series.
5.
If you rub ebonite and cat fur together which one becomes negative and
why?
 Ebonite becomes negative because ebonite is lower on the triboelectric
series.
LAWS OF ATTRACTION AND REPULSION
1. What do unlike (or opposite or dissimiliar)
charges do?

They attract.
What do like charges do?
2.

They repel.
What happens between a neutral object
and a positive object?
3.

The neutral object is attracted to the positive
object.
What happens between a neutral object
and a negative object?
4.

The neutral object is attracted to the negative
object.
1.
1.

2.

3.

Copy the following in your notebook and write if they would
attract or repel each other in the blank in the middle.
positive
attracts
negative
positive
repels
positive
positive
attracts
neutral
Negative
repels
negative
negative
attracts
positive
negative
attracts
neutral
Memorize and understand the laws of attraction and repulsion.
Opposite charges attract; Like charges repel; Charged objects
attract neutral objects.
What is Charles-Augustine de Coulomb famous for?
He made several important discoveries; 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. The metric
unit for electric charge is named the coulomb (C).
How many electrons are in 1 coulomb? You will need to
remember this number.
There are 6.24 x 1018 electrons in one coulomb.
ELECTRICAL INSULATORS AND CONDUCTORS
1. What is conductivity?

It is the ability of materials to allow electrons to move freely
in them.
What does an insulator do?
2.

It is a solid, liquid, or gas that resists or blocks the movement
of electrons.
If you wanted electricity to move from one location
to another location, would you use a conductor or
an insulator?
3.

I would use a conductor, because those materials allow
electrons to change positions.
If you had electricity traveling through a wire and
wanted to protect yourself from electric shock
what would you cover the wire in, aluminum or
rubber?
4.

I would cover the wire in rubber because it would not allow
the electrons (the electric shock) move freely.

2,
Friction is the force resisting the relative motion of two surfaces in
contact.
 When two neutral objects, like glass and cotton, are rubbed together,
electrons are transferred by the rubbing from the glass to the cotton.
This happens because glass tends to lose electrons more so than cotton,
because glass is higher on the triboelectric series. Glass ends up with a
positive charge, while cotton ends up with a negative charge.


3,


4 (but change the word “opposite” to “unlike”),


Opposite charges attract; like charges repel.
6,


A neutral object is NOT charged, but contains and EQUAL AMOUNT of
positive and negative charges (protons and electrons).
It could have an equal amount of protons to balance the charge.
7,
A conductor allows electrons to move freely, whereas an insulator
resists their movement.
 Any metal.
 Wood, plastic, rubber.

 8,


A fair conductor only allows SOME movement of
electrons.
The human body, soil, impure water.
9

Electric charges will spread through the water and
cause you injury.
 10,

They do not because neither one is higher or lower
on the triboelectric series, so neither one has a
larger tendency to gain or lose electrons.

11,
Pairs
cotton, steel
cotton, silk
human hair, human
hands (dry)
Teflon, wood
glass, plastic

Becomes More
Positively Charged
cotton
silk
human hands
Becomes More
Negatively Charged
steel
cotton
human hair
wood
glass
Teflon
plastic
13


You are sitting in a conductor, which makes it easily for
lightning to flow through. The water’s not pure either, so
it’ll make it easier for the charges in the lightning to flow
through that. Both are potentially dangerous/fatal.
Yes it would partially because you wouldn’t have to worry
about the lake killing you, as it is now an insulator.
What is an electroscope used for?
1.

It can detect static charge.
What are the thin metal flaps in an
electroscope called?
2.

They are called leaves.
Which law of charges explains why the
leaves of an electroscope separate when
a charged object is brought near it?
3.

Like charges repel.
What is electrostatics?
4.

It is the study of static electric charges.
 Draw
the following three electroscopes,
making sure that the number of electrons
illustrates what is happening.
A closed neutral electroscope.
 An electroscope that is separated with a negative
charge.
 An electroscope that is separated with a positive
charge.

CHARGING BY CONTACT
 When you charge a neutral object by
contact, what charge does the neutral object
get?

The same charge as the charged object.
1.

2.

3.

4.

5.

What is induction?
It is the movement of electrons within a substance caused by a
nearby charged object, without direct contact between the
substance and the object.
Why does rubbing a balloon on your hair make both the balloon and
the hair charged?
Electrons transfer from your hair to the balloon, meaning your hair
has more protons than electrons and is now positive, while the
balloon has more electrons than protons and is now negative 
charging by friction.
What type of material do you need to build up a static electric
charge, a conductor or an insulator?
An insulator.
If you bring a negatively-charged balloon near a wall but don’t
touch it, what charge does part of the wall get?
It gets a positive charge.
If you bring a negatively-charged balloon near a wall where do the
electrons in the wall go?
Further back into the wall because they are repelled by the
negative charges in the balloon.
What does “grounding” mean?
1.

It is the process of connecting a charged object to
Earth’s surface.
When you induce an electroscope with a
negatively-charged object, what charge
does the electroscope get?
2.

It gets a positive charge.
What do you need to do to make an
induced-charge permanent?
3.

You need to ground the electroscope while holding
the charged object near it to provide a path for
electrons to escape from the negatively-charged
object, or a path for electrons to get from the
ground closer to the positively-charged object.
ELECTRICAL DISCHARGE
1. When you get an electrical spark, does the
electricity discharge by contact, friction or
induction?

Induction.
LIGHTNING
1. What charge does a storm cloud normally
have, positive or negative?

It has a negative charge.
What charge does a storm cloud normally
induce in the ground?
2.

It induces a positive charge.
If a Van de Graaff generator has a lower
pully made of nylon and a belt made of
rubber, which part get negatively-charged,
the pully or the belt (look at the
Triboelectric series).
1.

Belt gets negatively charged.
If a Van de Graaff generator has a upper
pully made of Teflon and a belt made of
rubber, which part get negatively-charged,
the pully or the belt (look at the
Triboelectric series).
2.

Teflon gets negatively charged.

1,


2,



A negatively-charged object touches a neutral object.
A positively-charged object touches a neutral object.
3,


They are the same, electrical discharges.
It becomes temporarily charged because when the charged
object is brought near, the like charges are repelled by this
charged object, into the leaves, inducing an opposite
temporary charge (from the charged object) on the
electroscope.
4

While holding a charged object near the electroscope, use
your finger to ground the electroscope. Take your finger away
while still holding the charged object near. Then take the
charged object away, and your electroscope is now
permanently charged through induction.

6,



7,


Charges would have no path to travel down the metal
rod into the leaves.
8,



Electrons are being transferred in an electrical discharge
from you to the metal to the ground or vice versa. It will
make you neutrally charged. The shopping cart is
providing a path to or from the ground for the electrons
to use.
Again, the air is providing a path for electrons to travel
to the ground, neutralizing the cloud more.
This happens because like charges repel.
This happens because opposite charges attract.
9

The metal rod would receive the shock.
Why are large buildings fairly safe during a
lightning storm?
1.

They are safe because they will be properly
grounded if there is a strike.
What should you do during a lightning
storm in order to be safe in a car?
2.

Roll up the windows and don’t touch metal parts of
the car.
Why is it that men during the summer are
more often stuck by lightning than women
during the fall?
3.

Men are generally taller, making a shorter path for
the lighting to travel and more likely to be struck.
LIGHTNING RODS
1.
What part of the tree conducts the static discharge when a lightning
bolt strikes a tree?

The sap inside the tree conducts the electricity down to the ground.
GROUNDING STATIC CHARGES ON VEHICLES
1.
The textbook doesn’t say it, but when a moving car builds up a static
charge what are the two different types of materials that are rubbing
together?

Air and particles in it, and metal from the car. OR Rubber from the tires and
asphalt/cement/dirt/gravel from the ground
What device can you put on a car that “grounds” the car and prevents a
static charge from forming?
2.

A grounding strap grounds the car.
The textbook doesn’t say it, but when a moving plane builds up a static
charge what are the two different types of materials that are rubbing
together?
3.

Air and particles in it, and the metal on the plane are rubbing together.
What device can you put on a plane that “grounds” and prevents a
static charge from forming?
4.

Dissipaters are needle-like rods that disperse static charges into the air.
What type of material (insulator or conductor) do you use to prevent
static electric charges from forming?
5.

Conductors are used.
STATIC CHARGES AND FLAMMABLE MATERIALS
1.
Why is a car with a static electric buildup dangerous around gas stations?
 Gas is flammable and one static spark can ignite it.
REDUCING STATIC CHARGES IN THE HOME
1.
What would build up a larger amount of static cling, a load of dirty silk
clothes or a load of dirty silk and wool clothes?
 A load of dirty silk and wool clothes because they are made of different
material, so when they are rubbed together they will be charged by
friction.
2.
When do clothes in a drier build up a static charge – when the laundry is wet
or dry?
 More charges build up in dry air like during winter, because dry air acts as
an insulator.
3.
How do drier sheets reduce static cling?
 It 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.
4.
What are the four different methods for reducing charge build-up in a
computer room with a carpet?
 Use an antistatic mat for your feet; increase the moisture in the air with a
humidifier; spray the carpet with antistatic spray; wear an antistatic wrist
strap.








Why do industrial spray painters charge their spray paint with a negative charge?
 There is less waste due to bounce and overspray and the finish is smooth and
uniform.
Why don’t industrial spray painters get spray paint on the floor and walls behind the
object they are painting?
 The paint is attracted to the surface it is painting, because it is the opposite
charge of the paint. That attraction is so strong that it will be more attracted to
the object instead of neutral things around it.
In step 1, what is the charge on the selenium drum?
 It is positively charged.
When the selenium drum is in the dark does it behave as a conductor or an
insulator?
 Insulator.
When the selenium drum is in the light does it behave as a conductor or an
insulator?
 A type of conductor called a photoconductor.
What happens to the charge on the selenium drum when light is projected on it?
 The area on the drum becomes conductive and loses its charge, becoming
neutral.
What doesn’t happen to the areas of the selenium drum that is still dark when light
is projected on it?
 They do not become neutral and remain positively charged.
What charge is on the toner (ink)?
 It is charged negatively.
What does an electrostatic precipitator
do?
1.

Through the use of static electric charges, it
cleans gas by removing tiny pollutant particles
and sends clean gas out into the air. The
particles in the gas are charged when it is sent
through pipes, charging the particulate matter
negatively. The gas moves through an area with
positively charged plates, which attract the
negative pollutant matter and remove them
from the gas.

1 (you could get struck by lightning is not enough of an
answer – why is a tree more dangerous than a shrub?),


3,


It grounds the truck, allowing excess static charge to be
transferred to the ground so that the flammable liquid inside the
truck does not get ignited by an electric spark.
5,


Vehicles build up static charge through friction between the
vehicles outer surface and the air.
4,


Trees may be the highest point in the area, which makes it more
likely that it will be struck by lightning.
The paper may still be charged when it comes out of the
photocopier.
6

Antistatic dryer sheets, antistatic spray, electrostatic
precipitators, and photocopiers are four applications that use
electrostatic principles.

7,


8,


Through the third law, charged objects attract neutral objects.
11,


This is so your body does not transfer its charge into the metal tool, and
then into the electronic equipment, damaging it.
10,


When they are brought through pipes, the particulate matter becomes
negatively charged and so is attracted to the positively charged plate.
9 (how does the insulation protect the electronics?),


It is so large with so many positive and negative charges, that overall it
is not affected by any electron transfers and is considered neutral.
Water can be pure and therefore an insulator and not conduct
electricity; water is also only a fair conductor, and so it is not great at
conducting electricity at the best of times.
12

You could get rid of your carpet, use antistatic spray and antistatic
dryer sheets to reduce or eliminate these problems.
Why isn’t static electricity useful for operating
electrical devices?
1.

They build up and discharge, but they do not flow
continuously.
How do you want electrons to flow when you
operate an electrical device?
2.

You need a steady flow of electrons.
What are the two things that this section says
you need for a circuit?
3.

4.

The flow of electrons requires an energy source and
the path the electrons follow must be complete.
What is current electricity?
It is the continuous flow of electrons in a circuit.
What is an electrical load?
1.

It is a device that converts electrical energy to another form of
energy.
What does an electrical load do to electrical energy?
2.

It converts it to another form of energy.
List the four things you need to make an electrical circuit.
I have scrambled the letters of each one to help you
remember them. (reengy reoucs, ploceemt thap, chwist,
alod)
3.

Energy source, complete path (connector/conductor/wires),
switch, load
What is an open switch?
4.

5.

It means that there is a break in the path, so the electrons
cannot flow through the circuit.
What is a closed switch?
This means the circuit is complete and electrons can flow.
What is an electrochemical cell?
1.

It is a package of chemicals that converts chemical energy into
electrical energy that is store in charged particles.
What is a battery?
2.

It is a combination of electrochemical cells.
What is the difference between an electrochemical cell
and a battery?
3.

Battery contains many electrochemical cells.
Note: Usually an “electrochemical cell” is simply called a
“cell”.
A cell is made of two different electrodes. What happens
at each of the electrodes?
4.
5.

Electrons collect on one of the electrodes, making it negatively
charged. The other electrode has lost electrons, so it is
positively charged.
What does the electrolyte do in a cell?
6.

It reacts with the electrodes and conducts electricity.
 What
is the difference between a wet cell
and a dry cell?

Wet cells use a liquid electrolyte, while dry cells
use a paste electrolyte.
 Where

do you commonly find wet cells?
You find them in cars and other vehicles.
 Where
do you commonly find dry cells?
 You find them in flashlights, hand-held video
games devices, cameras, and watches.
RECYCLING AND RECHARGING DRY CELLS
 What do dry cells (common batteries) commonly
have in them that makes them bad for the
environment to simply throw away?
 They contain toxic materials like heavy metals,
including nickel, cadmium, and lead.
FUEL CELLS

What makes a fuel cell more reusable than
reusable batteries?
 The cell is not used up like ordinary cells would
be because as the electricity is produced, more
fuel is added.
What has more potential energy, an apple on a tree or an
apple that has fallen from a tree?
1.

The apple on the tree has more potential energy.
What is another term for potential difference?
2.

Another term for potential difference is voltage.
Explain what is meant by the term potential difference?
(this is very important to understand)
3.

The difference in electric potential energy between two points
in a circuit is termed potential difference or voltage. This
difference causes current to flow in a closed circuit. The greater
the potential difference in a circuit, the greater the potential
energy of each electron.
What is potential difference measured in (what units is it
measured in)?
4.

It’s measure in volts (V).

What is the name of the equipment that you measure
potential difference with?
It is called a voltmeter.
5.
1.

2.

When you turn on a circuit, do all the electrons along
the wire move towards the negative terminal or do
the electrons all have to start from the negative
terminal?
The electrons start from the negative terminal.
What is electric current?
It is a measure of the amount of electric charge that passes
by a point in an electrical circuit each second.
What is the difference between direct current and
alternating current?
3.

Direct current only flows in one direction, while alternating
current flows back and forth at regular intervals.
What is a common source of DC?
4.

A common source of DC is batteries.

What is a common source of AC?
A common source of AC is wall outlets or sockets.
5.
MEASURING CURRENT

What is the name of the equipment that you measure
current with?


You measure current with an ammeter.
What is the unit current is measured in?

Current (I) is measured in amperes or amps (A).
CURRENT ELECTRICITY AND STATIC ELECTRICITY

What is the difference between current and static
electricity in relation to current?
 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 given a path, but
does not continue to flow.
 What
colour is the positive terminal of an
ammeter?

It is red.
 What
colour is the negative terminal of an
ammeter?

It is black.
 What
terminal do you connect the red terminal
of an ammeter to when measuring current in a
circuit?

You connect it to the positive terminal.
 What

is resistance?
It is the degree to which a substance opposes the
flow of electric current through it.
 What
type of substance has more resistance,
a conductor or an insulator?

An insulator has more resistance.
 What

unit is resistance measured in?
It is measured in ohms (Ω).
 What
does resistance do to the energy in
electricity, use it up or push it backwards?
 It uses it up, converting the electrical energy
into other forms of energy.

What is a resistor?


Why does the filament in a light bulb produce light?


It has a high resistance to the electron’s electrical energy
and that causes it to heat up and produce light.
When does a circuit have a higher potential
difference, before it enters a resistor or after it
enters a resistor?


It is a material that can slow current flow.
It has a higher potential difference before it enters a
resistor.
What happens to a circuit’s potential energy when
the electrons leave a resistor?
 The potential energy has been converted to another
form of energy, and so it decreases.
 List
some of the materials that resistors are
made out of.


Some materials that resistors are made out of
are heat-resistant metal with insulating cores, as
well as those materials mixed with carbon.
What would have less resistance, a thick
wire or a thin wire?

A thin wire would have more resistance because
there is not as much space for the electrons to
get through.
1.
2.
3.
4.
5.
They are composed of an electrolyte and two
electrodes; an electrolyte can be a liquid or a paste
that conducts the electricity produced by the
ionization of the electrodes, usually zinc and copper.
A reaction is produced between the electrolyte and
electrodes in a wet cell, which creates electricity.
They flow from the negative end of the source to the
positive end.
Voltmeters measure potential difference.
Potential difference it measured in volts (V).
Ammeters measure current.
Current is measured is amperes or amps (A).
Potential difference is the pushing force of electrons,
while current is the number of moving electrons.
1.
2.
3.
4.
5.
DC flows only in one direction, while AC flows back
and forth in intervals.
An electric load converts electrical energy into
another type of energy (i.e. heat, light, sound, etc).
Some examples of electrical loads are lights, motors,
and resistors.
It is the degree to which a substance opposes the
flow of electrons through it.
It slows down the movement of electrons and
converts the electrical energy into other forms of
energy.
The four factors affecting resistance in a wire are the
following: the material, the cross-sectional area or
thickness, the length, and the temperature.
What are the two rules you need to follow when drawing a
circuit diagram?
1.


Always use a ruler to draw straight lines for the conducting
wires.
Make right-angle corners so that your finished diagram is a
rectangle.
What is wrong with the circuit diagrams shown here?
2.



The first rule isn’t obeyed.
The second rule isn’t obeyed.
No electrical symbols are used.
For practice, draw and label each of the symbols for the
following components found in a circuit diagram.
3.
wire
 battery
 light bulb
 resister
 switch
 voltmeter
 ammeter

What is a series circuit? Write down the second sentence,
the one that starts, “A series circuit has only one …”
1.

…path along which electrons can flow.
Recall that current is the amount of electrons flowing
through a circuit each second. In a series circuit is the
current at the end of the circuit less, the same or more
than the current at the beginning of the circuit?
2.

The TOTAL current is the same.
Does adding more resistance in a series circuit increase or
decrease the current?
3.

4.

Adding more resistance will decrease the TOTAL current.
If you add more lights in a series circuit does that make
the light brighter or dimmer or do they stay the same?
Adding more lights will make all the lights dimmer in a series
circuit.

What is the full explanation of a parallel circuit?


If one path in a parallel circuit is cut, will the rest of the
circuit still be able to work?


It decreases the total resistance of the circuit.
What does most of the current in a parallel circuit go
through, the path with the most resistance, all paths equally
or the path with the least resistance?


Yes, it will still be able to work.
Does the addition of a new path in a parallel circuit
increase, keep the same or decrease the total resistance?


It is an electric circuit in which the parts are arranged so that
electrons can flow along more than one path.
Most of the current will pass through the path with the least
resistance.
What is the same along each path in a parallel circuit, the
voltage, the current or the resistance?
 The voltage is the same along each path in a parallel circuit.
1.
Complete the following table:
Series Circuit
Number of paths one path
for electrons to
travel
Current
stays the same
Voltage
Parallel Circuit
more than one path
divides into different
paths, with the pathway
with less resistance
having a greater current
divides into the different loads stays the same
 What
is the current at each of the points of
the following circuits?
I1=5A
I4=5A
IT = 5 A
I23=5A
I5=5A
IT= 5A
I1= 2A
I2=3A
 What
is the voltage at each of the points of
the following circuits?
V4=4V
V1= 1V
VT= 10V
V23= 3V
V5= 2V
VT= 5V
V1= 5V
V2=5V
Draw circuit diagrams for circuits with the following.
 A series circuit that has:
 1x cell
 3x lights
 1x open switch
 A series circuit that has:
 1x 2-cell battery
 1x motor
 1x resister
 1x closed switch
 A series circuit that has:
 2x 3-cell batteries
 3x lights
 1x open switch
 A parallel circuit that has:
 2x 3-cell batteries in series
 2x lights (each in parallel)
 2x open switches (each switch controls one light)
 A parallel circuit that has:
 2x 3-cell batteries in parallel
 2x resisters in parallel
 1x open switch (that controls both lights at the same time)

Why is the letter “I” used for current? (see box
“words matter”)


What is the full name of the high school teacher who
first worked out Ohm’s Law?


The high school teacher’s name is Georg Simon Ohm.
Ohm’s law is true so long as what stays the same?


The symbol “I” is used for current because it stands for
INTENSITY.
As long as the temperature stays the same, Ohm’s law
will hold true.
Complete the three equations:



V = IR
I = V/R
R = V/I

A current of 4.0 A flows through a 40  resister in a circuit. What
is the voltage?
Given – I = 4.0A, R = 40 
 Required – V = ?
 Analysis – V = IR
 Substitution and Solution



V = IR
V = (4.0A)(40)
V = 160V

Paraphrase – The voltage in this circuit is 160V.
A 30 V battery generates a current through a 15  resister. How
much current does the battery generate?
Given – V = 30V; R = 15
 Required – I = ?
 Analysis – I = V/R
 Substitution and Solution

I = V/R
 I = (30V)/(15)
I = 2A
 Paraphrase – The battery generates 2A of current.


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 – V = 240V; I = 20A
 Required – R = ?
 Analysis – R = V/I
 Substitution and Solution

R = V/I
 R = (240V)/(20A)
 R = 12



Paraphrase – The resistance of the heating element is 12.
A current of 1.5 A flows through a 30  resister that is connected
across a battery. What is the battery’s voltage?
 Given – I = 1.5A; R = 30
Required – V = ?
 Analysis – V = IR
 Substitution – V = IR = (1.5A)(30) = 45V
 Paraphrase – The battery’s voltage is 45V.


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?
 Given – R = 15; I = 0.60ARequired – V = ?
 Analysis – V = IR
 Substitution – V = IR = (0.60A)(15) = 9V
 Paraphrase – The voltage across the headlight is 9V.
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?
 Given – R = 60; V = 24V Required – I = ?
 Analysis – I = V/R
 Substitution – I = V/R = (24V)/(60) = 0.4A
 Paraphrase – The current in this circuit is 0.4A.
A bulb of 15  resistance is in a circuit powered
by a 3 V battery. What is the current in this
circuit?
 Given – R = 15; V = 3V Required – I = ?
 Analysis – I = V/R
 Substitution – I = V/R = (3V)/(15) = 0.2A
 Paraphrase – The current in this circuit is 0.2A.
 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?
 Given – I = 0.75A; V = 3.0V
Required – R = ?
 Analysis – R = V/I
 Substitution – R = V/I = (3.0V)/(0.75A) = 4
 Paraphrase – The bulb’s resistance is 4.

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?
 Given – I = 625mA = 0.625A; V = 120V
 Required – R = ?
 Analysis – R = V/I
 Substitution – R = V/I = (120V)/(0.625A) = 192
 Paraphrase – The resistance of the bulb is 192.
 What would the current be if the resistance was
45  using a 3 V battery?
 Given – R = 45; V = 3V Required – I = ?
 Analysis – I = V/R
 Substitution – I = V/R = (3V)/(45) =0.067A
 Paraphrase – The current would be about 0.067A.


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?






Given – I = 200mA = 0.200A; V = 120V
Required – R = ?
Analysis – R = V/I
Substitution – R = V/I = (120V)/(0.200A) = 600
Paraphrase – The resistance for the table lamp is 600.
The current in a circuit is 0.50 A. The circuit has two
resisters connected in series: one is 110  and the other is
130 . What is the voltage in the circuit?
Given – I = 0.50A; R = 110 + 130 = 240
 Required – V = ?
 Analysis – V = IR
Substitution – V = IR = (0.50A)(240) = 120V
 Paraphrase – The voltage in the circuit is 120V.

 How
does temperature change the resistance
of a material?

Resistance is lower when a conductor is cooler,
while when the temperature increases,
resistance increases.
 Why
do incandescent bulbs often burn out
within the first millisecond of turning them
on?
 They do this because of the sudden
temperature change and other forces caused
by the large initial current.
 How
does temperature change the resistance
of a material?


Resistance is lower when a conductor is cooler,
while when the temperature increases,
resistance increases.
Why do incandescent bulbs often burn out
within the first millisecond of turning them
on?
 They do this because of the sudden
temperature change and other forces caused
by the large initial current.

If you are trapped in a car with a live wire
touching the car (as in Figure 11.39 pg 462) why
is it safer to remain in the car than to walk out?


It is safer to remain in the car than to walk out
because if you come in contact with the wire, the
electricity will take a path through your body to the
ground and seriously injure or cure you.
If you are trapped in a car with a live wire
touching the car (as in Figure 11.39 pg 462) why
is it safer to jump out of the car than to walk
out?
 It is safer to jump out rather than walk would so
that he does not provide a path for the
electricity to flow through him to the ground.

What happens to a fuse if there is too much current flowing
through it?


Which type of metal would it be better to make a fuse out
of if you want the fuse to be sensitive, lead (melts at low
temperatures) or iron (melts at high temperatures)?


Lead would be better because it has a low melting point.
What does a circuit breaker and a fuse do that is similar?


If the current gets too high, the metal in the fuse melts and the
current flow stops, which helps to prevent further problems,
such as damage to your electrical components or a possible fire.
It does the same job as a fuse (turns off the circuit), except that
the wire inside does not melt. A circuit breaker is more modern.
If a circuit breaker does not melt and turn off a circuit, what
does it do to turn the circuit off when there is too much
current?
 The wire heats up and bends, which triggers a spring
mechanism that turns off the flow of electricity.

What does the third round prong on a three-prong plug do with
unwanted electricity?


What do the other two prongs do? (The answer is not in the
textbook – but you can figure it out – Hint: what are the two ends
of a battery)


One side is negative, releasing electrons and carrying the current to the
load, while the other side is positive, returning the current to the
source.
What is the short form for ground fault circuit interrupter?


It connects the device to the ground wire of the building, sending any
unwanted current flow directly to the ground.
The short form is GFCI.
Why when you go home will you usually only find GFCI’s in your
kitchen and bathroom?

You usually only find GFCI’s in the kitchen or bathroom because
water is used most often there, allowing current to flow more
freely if it comes into contact with the water. The GFCI will notice
this and open the circuit so there is less chance of injury to you.