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MEASURING AND USING
ELECTRICITY
From
Electricity and Magnetism
A Unit of Study
Produced by
Colgren Communications
Written by
John Colgren
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© 2004 Colgren Communications
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . .1
Instructional Notes . . . . . . . . . . . . . . . . .1
Links to Curriculum Standards . . . . . . . . .2
Student Objectives . . . . . . . . . . . . . . . . .3
Assessment Tools . . . . . . . . . . . . . . . . . . .3
Unit Test . . . . . . . . . . . . . . . . . . . . . . . . .3
Teacher Preparation . . . . . . . . . . . . . . . . .4
Introducing the Program . . . . . . . . . . . . .4
View the Program . . . . . . . . . . . . . . . . . . .4
Discussion Questions . . . . . . . . . . . . . . . .4
Description of Blackline Masters . . . . . . .4
Enrichment Activities . . . . . . . . . . . . . . . .5
Answer Key . . . . . . . . . . . . . . . . . . . . . . . .6
Internet Resources . . . . . . . . . . . . . . . . .9
Script of Narration . . . . . . . . . . . . . . . . .9
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MEASURING AND USING ELECTRICITY
from
Electricity and Magnetism A Unit of Study
Grade Levels: 5-8
Viewing Time: 15 minutes
INTRODUCTION
This live-action program is designed for use with the intermediate grade levels (5-8).
This program is about how we measure electricity. Terms covered in the program include voltage, wattage, current, and
amperage. Directions are given for determining the wattage
and amperage of common household utensils and appliances.
The power company keeps track of how much electricity its
customers use by reading electric meters. Circuit breakers are
used to protect the electrical circuits in a house or business.
INSTRUCTIONAL NOTES
Before presenting this lesson to your students, we suggest that
you preview the program and review this guide and the accompanying blackline master activities in order to familiarize yourself with their content.
As you review the materials presented in this guide, you may
find it necessary to make some changes, additions, or deletions
to meet the specific needs of your class. We encourage you to
do so, for only by tailoring this program to your class will they
obtain the maximum instructional benefits afforded by the
materials.
It is also suggested that the program presentation take place
before the entire group under your supervision. The lesson
activities grow out of the context of the program; therefore, the
presentation should be a common experience for all students.
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LINKS TO CURRICULUM STANDARDS
This Unit of Study addresses the following National Science
Education Standards for grades 5-8:
Science as Inquiry
Content Standard A:
• Abilities necessary to do scientific inquiry
Plan and conduct simple investigations.
Employ simple equipment and tools to gather data.
Use data to construct a reasonable explanation.
Communicate investigations and explanations.
• Understanding about scientific inquiry
Physical Science
Content Standard B:
• Energy is a property of many substances and is associated
with heat, light, electricity, mechanical motion, sound, nuclei,
and the nature of a chemical. Energy is transferred in many
ways.
• Electrical circuits provide a means of transferring electrical
energy when heat, light, sound, and chemical changes are produced.
Science and Technology
Content Standard E:
• Abilities of technological design
• Understanding about science and technology
People have always had questions about their world.
Science is one way of answering questions and explaining
the natural world. People have always had problems and
invented tools and techniques to solve problems.
Scientists and engineers often work in teams.
Tools help scientists make better observations, measurements, and equipment for investigations.
History and Nature of Science
Content Standard G:
• Science as a human endeavor
Science and technology have been practiced for a long time.
Men and women have made a variety of contributions
throughout the history of science and technology.
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Although men and women using scientific inquiry have
learned much about the objects, events, and phenomena in
nature, much more remains to be understood. Science will
never be finished. Many people choose science as a career
and devote their entire lives to studying it.
STUDENT OBJECTIVES
After viewing the program and participating in the lesson activities, the students should be able to do the following:
• Define terms such as voltage, wattage, amperage, and current.
• Distinguish between alternating and direct current.
• Define the three components of a circuit.
• Describe how the power company keeps track of electrical
consumption through the use of electric meters.
ASSESSMENT TOOLS
This lesson provides you with three different assessment tools.
Together they make it possible to closely follow the progress of
your students and to judge their mastery of the subject matter.
The Pre-Test (Blackline Master 1) can be used to get some
idea of students' understanding of the topic before the program
is presented.
The Program Quiz and its accompanying answer sheet
(Blackline Master 2) can be used either as a way to introduce
the topic prior to showing the program or to judge student mastery once the program has been presented
The Post-Test (Blackline Master 8) can be used as a final test
for the lesson.
UNIT TEST
An optional Unit Test has been provided with this lesson. It can
be used as a final test to gauge student comprehension of the
material presented in all five lessons of this Unit of Study.
Answers to the Unit Test are provided in the Answer Key of this
instructor’s guide.
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TEACHER PREPARATION
View the program and review the accompanying activities.
Duplicate any blackline masters you wish to distribute. If you
plan to use the Program Quiz, which immediately follows the
program presentation, you may wish to have copies of the quiz
ready to distribute at the completion of the program. Also, plan
to pause the tape between questions if students require more
time.
INTRODUCING THE PROGRAM
Ask the students if anyone knows how the electric company
keeps track of how much electricity is used by its customers.
Tell the class that there are ways to describe the flow of electrons and the movement of electricity. This program will
describe and define the terms associated with the use of electricity. It will also tell how circuit breakers protect our homes.
VIEW THE PROGRAM
Viewing time for this program is 15 minutes. The program quiz
that follows the presentation will take about three minutes when
you build in pauses for recording answers.
DISCUSSION QUESTIONS
You may wish to conduct a discussion after viewing the program based on the following:
1. Why is it important to be careful about the number of electrical appliances plugged into the same circuit?
2. Why are octopus plugs a bad idea?
DESCRIPTION OF BLACKLINE MASTERS
This program contains eight blackline masters that can be used
to reinforce ideas and information presented in the program.
• Blackline Master 1, Pre-Test, provides a way of finding out
how much students know about the material covered in this les4
son before you present it. Students’ scores on the Pre-Test can
be compared with their scores on the final Post-Test (Blackline
Master 8).
• Blackline Master 2, Program Quiz, is to be used at the end
of the program. At the completion of the program, there is a
short quiz. The narrator will read the questions which are displayed on the screen. Students can use Blackline Master 2 to
record their answers. Answers to the questions are provided in
the Answer Key section of this instructor's guide.
• Blackline Master 3, Rheostats, is an experiment for demonstrating how a rheostat works. A rheostat is used in dimmer
switches.
• Blackline Master 4, Electric Power, describes how electric
power is calculated. Students are given questions to answer
concerning common household appliances.
• Blackline Master 5, Electric Meter, is an information sheet
about reading electric meters. Students are to calculate the
amount of electrical energy their family uses in a 24-hour period.
• Blackline Master 6, Watts Cooking?, and Blackline Master
7, Watts Cooking?, Part 2, go together. Students are asked to
locate various electrical appliances around their homes and then
fill in the missing information of page 2 using the formulas
described on page 1.
• Blackline Master 8, Post-Test, is an evaluation tool for this
unit.
ENRICHMENT ACTIVITIES
1. Have some students examine their power bills to locate the
rate and charges for a month. Electricity is one of our cheapest
forms of energy.
2. You may want to examine the monthly electrical charges for
your school. Have the students determine some ways to reduce
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that expense. Consider posting signs in classrooms to turn off
lights when the room is not in use, or maybe a poster campaign
to help others consider power saving ideas for school and home.
ANSWER KEY
• Blackline Master 1, Pre-Test
I. Matching
1. b
6. h
2. g
7. j
3. e
8. d
4. f
9. l
5. a
10. c
II. Short Answer
1. If the amperage of the circuit increases beyond its limit, the
circuit breaker turns off to stop the flow of electricity.
2. The circuit breaker protects the circuit from too much current. If the breaker didn't stop the flow of electricity, the circuit
could overheat and start a fire.
3. A hair dryer has a filament that resists the flow of electrons,
so the filament heats up. A fan behind the heated filament
blows the heated air out the nozzle of the dryer to dry your hair.
• Blackline Master 2, Program Quiz
Part A: Multiple Choice
1. b
4. b
2. a
5. c
3. d
6. d
Part B: Short Answer
1. A circuit breaker turns off the flow of electricity so that the
circuit doesn't overheat and cause a fire.
2. 720 watts divided by 120 volts equals 6 amps.
3. Copper is a good conductor of electricity because of the
structure of the copper atom. The copper atom has a loosely
held electron in its outer orbit.
4. An open circuit means that the circuit is broken or disconnected.
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• Blackline Master 3, Rheostats
Observations:
1. The brightness of the bulb changes as the wire slides up and
down the pencil lead.
2. The light is brightest when the wire is closest to the end of
the pencil end that has the second wire connected to it.
Conclusion:
The rheostat works because there is a material made of a resistor. The resistor slows the flow of electrons so a lamp will dim
as fewer electrons go through its filament.
• Blackline Master 4, Electric Power
1. 6 x 120 = 720 watts
2. 120 x 2.5 = 300 watts
3. 1080/120 = 9 amps
4. 2400/120 = 20 amps
• Blackline Master 5, Electric Meter
Answers will vary.
• Blackline Masters 6 and 7, Watts Cooking
Answers will vary depending on the appliances each student
chooses to investigate.
• Blackline Master 8, Post-Test
I. Circle the word
1. electrons
2. ampere
3. watts
4. volts
5. direct current
II. Short Answer
1. Light bulbs use filaments that resist the flow of electricity.
The electrons slow down and cause the filament to glow.
Toasters use filaments to heat up and toast bread.
2. The electricity going into a home or business goes into an
electric meter first. The meter has five dials that keep track of
the kilowatts of electricity going through the meter.
3. Direct current is the kind of current produced from wet and
dry cells. This current flows in one direction. Alternating cur7
rent is produced at power plants. The current alternates, or
moves in one direction and then reverses and moves in the other
direction.
4. A power plant spins a magnet in a coil of wire or spins a coil
of wire in a magnetic field. In the example seen in the program,
we could see that as the magnet moves in and out of the coil of
wire, the needle on the voltmeter moved one way and then the
other way.
5. a. 10 amps c. 8 amps
b. 1 amp d. 13 amps
• Unit Test
I. Matching
1. d
2. h
3. f
4. a
5. i
6. g
7. c
8. e
9. b
II. Short Answer
1. copper, silver, gold
2. wood, glass, rubber, cloth, plastic
3. Insulators are used to stop the flow of electricity. Insulators
around a wire will stop the electricity from moving out of the
wire and into another conductor.
4. A generator produces electricity. It is made of either a coil of
wire spinning in a magnetic field or a magnet spinning in a coil
of wire. In either case, a flow of electrons is created.
5. An electromagnet can be made with a source of electrons,
some wire, and an iron nail. Wrap the wire around the nail.
Connect the wire ends to the terminals of the battery and you
have an electromagnet.
6. An electromagnet can be turned on and off, but a regular bar
magnet can't.
7. A source of electrons, a path for the electrons to flow along,
and something to use the electrons.
8.
battery
battery
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9. A series circuit has one path one which electricity flows. If a
bulb in a series circuit burns out, all the lights go out. A parallel circuit has two paths on which electricity flows. If one bulb
burns out, there is still a path for the electricity to flow along,
so other bulbs in the circuit stay lit.
10. Fuses and circuit breakers will automatically trip, or stop,
the flow of electricity if the circuit becomes overloaded by the
flow of current.
11. Answers will vary.
12. The sun's energy through the use of solar cells, wind turbines, geothermal energy, chemical energy
13. They would move apart because they would be repel-led.
14. They would come together because they are attracted.
15. a. 4 amps
b. 8 amps
c. 6 amps
INTERNET RESOURCES
The following websites may be valuable sources of additional
information to reinforce the objectives of this lesson:
1. "What Is Electricity?" by Energy Information Admin-istration.
http://www.eia.doe.gov/kids/electricity.html
2. Clark County Public Utilities in the state of Washington has
a wonderful site with excellent pages on topics related to electricity.
http://clarkpud.apogee.net/kids/
3. Energy Story at the Energy Quest Site.
http://www.energyquest.ca.gov/story/index.html
SCRIPT OF NARRATION
Electric current is a continuous flow of charge through a wire.
It is the rate of charge past a certain point. The greater the current, the more charge that passes that point. Current is measured in amperes, or amps, for short.
9
Think of it like a water hose. The water coming out the nozzle
is like current. A certain amount of water passes through the
nozzle at a given moment. If more water is needed, then the
flow is increased and more water goes whooshing past the nozzle. The water is like current and amps are used to measure how
much of the current goes past a point in a given amount of time.
The greater the current, the higher the amperage.
There are two types of current. One is called alternating current, or ac, for short. The other is direct current, or dc.
Direct current is the kind of current we get from batteries. This
kind of current always travels in the same direction.
Alternating current is the kind used in homes, businesses, and
schools. This kind of current is developed at a power plant.
It is used because it is easier to send from the power plant to
places that will use the electricity.
It is called alternating current because it is produced when magnets spin in a coil of wire. Michael Faraday found out in 1831
that when a magnet moves in a coil of wire, an electric current
is produced. If we look closely at the movement of the magnet
and compare that with what is happening with the voltameter
needle, we see that when the magnet goes into the coil, the needle moves one way; and when the magnet is pulled out, the needle moves the other way. So as the magnet moves in the coil,
the current alternates between two different directions.
In the United States, the current alternates at the rate of 120
times per second for 60 complete cycles per second.
For a flow of electricity to occur, we must have what is called
a complete circuit. A circuit is made up of three parts. A source
of electrons, a path for the electrons to travel along, and a
device to use the electrons. We can make a simple circuit using
these materials: a battery, some wire, and a flashlight bulb. The
battery will provide a supply of electrons. The wire will form
the path from the battery to the bulb and then back to the battery. When everything is connected, the bulb lights up.
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The current flows from the negative terminal of the battery
through the wire to the bulb and then back to the positive pole
of the battery. The path must be complete without any breaks,
or gaps.
When there is a break in the circuit, the circuit is said to be open
and the light goes out.
When the circuit is closed and no gaps are present, the bulb
lights.
Switches are added to circuits to make it easier to open and
close the circuit, and therefore, control the flow of current.
Current must always flow in a complete circle from the source
of electrons through the electrical device and back to the source
of electrons.
This is true for circuits in homes, schools and businesses as
well. Notice that the outlet has two vertical holes, or slits, and
one smaller round hole.
The round hole is for grounding electrical devices that you plug
into the outlet. This way there will be less of a chance for electrical failures and damage done by short circuits.
The two vertical slits are for the prongs of the electric cord of
an appliance. The current flows along one prong and into the
device and then back out of the device and through the other
prong into the other outlet slit.
You may be wondering why the power cord prongs have holes
in them. Well, inside the outlet are little ball clips that pop into
those holes and help hold the prongs in the outlet.
The wires are made of a good conductor which loses electrons
from its atoms.
For instance, atoms of copper have a weakly held electron in
their outer electron shells. That means the electrons in orbit
around the nucleus of copper atoms are loosely held and can be
pushed out of orbit when a free electron comes near its orbit.
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Now that released electron can move to another copper atom
and cause its outer electron to jump away. This is repeated over
and over again as the current is flowing through the circuit.
VOLTAGE
The push behind the current is called voltage and is measured
in volts.
You have probably seen dry cells marked as one-and-a-half
volts.
If a flashlight bulb is rated as a three-volt bulb, it would only
dimly light if we connect the dry cell to it.
But if we attach two one-and-a-half dry cell batteries together
like this, we will increase the overall voltage to three volts and
the bulb lights brightly.
WATTAGE
The amount of electrical energy used in a certain amount of
time is measured in what is called watts. Wattage is the measure of electrical use multiplied by time.
So a 100-watt bulb burning for 10 hours uses 1,000 watts of
energy. A thousand watts is called one kilowatt.
The power company keeps track of how much electrical energy
a home or business is using by reading electric meters, which
are often found outside a building. The main electrical wire
from the power company goes to the electric meter and then
into the circuit box of the building.
The electric meter has five dials, each with ten numbers from 0
to 9 written on them. An arrow on each dial moves around as
more and more electric current flows through the meter. See
the disk spinning. That disk is recording the flow of current
into this home. It will spin very fast if a lot of electrical devices
are being used at the same time.
If everything in the home that ran on electricity were to be
turned off and unplugged, then the disk wouldn’t move at all.
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The dials are read by someone from the power company and the
number is recorded.
Then the next time the person from the power company reads
the dials, a new number is recorded.
The first reading is subtracted from the second reading and a
total for how many kilowatt hours of electricity have been used
during that time period is established.
The first dial on the far right is the ones column. The next dial
is for the tens column and so on until the last dial represents the
ten thousands place.
Electrical consumption is measured in kilowatt hours. So if the
power company charges ten cents per kilowatt hour, that 100watt light bulb burning for ten hours costs ten cents.
After the electric wires go into the electric meter, they go into
the building’s circuit box. This box then provides a series of
separate circuits for the electric current to flow through.
For instance, the clothes washer and dryer will probably need
greater push to do the kind of electrical work they are designed
to accomplish. So a special 240-volt circuit is set up for those
electrical devices.
Notice the plugs for the clothes washer is different from other
plugs.
Other circuits in the home will need typical 120-volt connections and outlets.
So circuits are set up to run into different parts of the home to
prevent one circuit from becoming overused.
You see, the more electrical appliances that are plugged into a
circuit and turned on, the greater the need for a greater flow of
current. The more current that is flowing, the greater the danger of overloading the circuit and causing a fire.
13
Circuit breakers are designed to allow a certain amount of
amperage to build up in a circuit. For instance, a circuit may be
designed for 20 amps. That means that as long as the amperage
in that circuit stays below 20, the flow of current will continue.
However, if the amperage goes above 20, then the circuit breaker trips and the flow of current is stopped. You may have experienced that when using a bunch of electrical devices at the
same time. Suddenly everything stops. That’s an indication that
the circuit has been overloaded and the amperage has risen
above the circuit’s limit. This is a safeguard because the wires
in the circuit have been getting hotter and hotter, and if the circuit breaker didn’t trip, a fire might have resulted.
To correct the situation when everything shuts down, unplug
some of the appliances and then reset the circuit breaker by flipping it back to the on position.
Wattage is a measure of how much electrical energy a device
needs to operate. Some devices have high wattage requirements and some have very small needs.
For instance, this 1,200-watt hair dryer needs more energy than
this 100-watt light bulb.
The hair dryer uses a wire that resists the flow of electrons; and,
as a result, glows red hot and gives off heat. Behind the wire is
a motorized fan to blow the hot air towards your wet head. A
lot of energy is needed to get the wires to give off all that heat
and for the fan to operate properly.
This light bulb also has a wire that resists the flow of electrons
and turns bright as a result. However, the tungsten wire in the
filament of the light doesn’t need a lot of current so it’s wattage
is low.
A 60-watt bulb isn’t as bright as a 100-watt bulb.
Amperage is the measure of current. To calculate amperage,
you can divide the wattage of a device by the voltage that it
requires.
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So the amperage for the 100-watt light bulb is less than one.
In a 20-amp circuit, we could have twenty 100-watt light bulbs
plugged in and on without tripping the circuit breaker.
However, the hair dryer rated at 1,200 watts will have an
amperage of 10 amps. That means in a 20-amp circuit, we can’t
have other devices that use a lot of amps plugged in and turned
on at the same time as we use the hair dryer; otherwise, the circuit breaker may trip.
You can find the wattage of most electrical devices on a special
identification plate found on the back, side, or bottom of the
appliance.
Let’s look at a few common appliances and compare their
wattage. Remember, the higher the wattage, the greater the
amperage. Things with high amperage shouldn’t be plugged in
at the same time.
Now it is time for the program quiz. The first six questions are
multiple choice and the final four questions are short answer.
1. Current is measured in ________________.
volts
amperes
electrons
protons
2. The push behind current is called ____________.
voltage
amperes
electrons
wattage
3. The amount of electrical energy used in a certain amount of
time is called _______.
voltage
amperes
electrons
wattage
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4. Materials that allow the flow of electricity are called
_________.
insulators
conductors
wattage
voltage
5. A complete circuit is made up what three things?
voltage, wattage, and amperes
conductors, insulators, circuits
source of electrons, a path, something to use the eletrons
electrons, protons, and neutrons
6. A thousand watts is called one _________________.
circuit
one hundred-twenty volts
sixty cycles
kilowatt
Part B Directions: The next four questions are short
answer.
7. How do circuit breakers protect our homes?
8. If a household appliance has a wattage of 720 and it uses
standard 120 volts, what would the amperage be for this
device?
9. Why is copper such a good conductor of electricity?
10. What does it mean when the circuit is open?
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