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Inquiry
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Jackson County Mathematics and Science Center
Copyright August 2002, by Jackson County Intermediate School District. Permission is granted to local school districts
and institutions of higher education in Jackson County, Michigan to reproduce these materials for their own use.
Learning About Electricity
Introduction
At the elementary level, the State Science Benchmarks for electricity include one benchmark about
constructing circuits that work, one about electrical safety, and one that includes electricity as a form of
energy:
IV.1.E.4 Construct simple, useful electrical circuits. (3-5)
Key concepts and tools: Complete loop; batteries, bulbs, bells, motors, wires, electrical switches (see
PME-IV.1 e.2, materials that conduct electricity).
Real-world contexts: Flashlights, battery-powered toys.
IV.1.E.5 Describe possible electrical hazards to be avoided at home and at school. (K-2)
Key concepts: Shock, wall outlet, hazards; see PME-IV.1 e.3 (electrical energy).
Real-world contexts: Electric outlets, power lines, frayed electric cords, electric appliances, lightning, hair
dryers in sinks and tubs.
IV.1.E.3 Identify forms of energy associated with common phenomena.
Key concepts: Heat, light, sound, food energy, energy of motion, electricity (see PCM-IV.2 e.1 about heat,
PWV-IV.4 e.1-4 about light and sound, PME-IV.1 e.4 about electricity, LEC-III.5 e.2 about energy from
food).
Real-world contexts: Appropriate selection of energy and phenomena, such as appliances like a toaster or
iron that use electricity, sun’s heat to melt chocolate, water wheels, wind-up toys, warmth of sun on skin,
windmills, music from guitar, simple electrical circuits with batteries, bulbs and bells.
Benchmark IV.1.E.4 is really a performance task for students: They need to actually construct simple circuits
that work. There isn’t much abstract knowledge in this benchmark, other than the conclusion that a complete
loop is needed to make a working circuit. Students are not required by this benchmark to know, for instance,
how a series circuit is different from a parallel circuit, or what voltage, current and resistance are. They don’t
need to differentiate between conductors and non-conductors or open and closed circuits, although using
those terms is probably unavoidable, and helpful, when they think about how bulbs and switches get
connected. What students do learn that is a bit theoretical, along the way to understanding what a complete
loop is, is that electricity moves in a circuit in order to go from the battery to the bulb, where it is needed to
make the bulb light. It can’t move unless a wire (a conductor) gives it a path to and from the bulb (or bell or
motor).
Students aren’t required by the benchmark to know how a battery works, either. They should recognize,
however, that a battery is a source of electrical energy, just as a wall socket is – and they should learn that
wall sockets are much more dangerous than batteries because they provide much more powerful electricity.
There are several ways to attach a battery to a light bulb – many don’t work. The important
task for students is to try different ways of attaching the battery and bulb until they find a
way that works, drawing each different approach. Then they should draw a conclusion
from their investigations about how batteries and bulbs need to be connected.
In steps 1 and 2 of the first activity, students are asked to examine their batteries and bulbs
and make careful drawings of what they notice about them. They need to recognize that
batteries have two “working” ends (the positive and negative terminals) and that bulbs also
have two places for attaching wires – the bottom metal knob and the sides of the metal
base. The bottom knob is insulated from the sides by non-metallic material that does not
conduct electricity.
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Learning About Electricity
Caution students not to connect one end of a battery to its other end directly with a wire. This causes
the wire to get very hot and the battery to wear out very quickly.
Figuring out how to connect batteries and bulbs so that they work is an inquiry activity because:
1) students are given a question to investigate;
2) they gather data (their trials and drawings); and
3) they draw a conclusion from their data.
They should be responsible for communicating their conclusions to each other or another audience (parents
perhaps).
The conclusion that follows from the data they collect is that a complete loop is needed to make a bulb light
(or a motor spin, buzzer sound, etc.) Since this phrase (“complete loop”) is included in the Key Concepts for
the elementary benchmark, you should help elementary students to understand what a complete loop is and
encourage them to use the term. They need to be fluent with the term and the idea of a complete loop when
they take the MEAP test. The loop goes from one end of the battery, into the bulb (or motor, etc.) out the
other side of the bulb and back to the other side of the battery. This loop carries the electricity. In other
words, the electricity goes from one end of the battery through the bulb and back to the other end of the
battery. Students look carefully at their battery and bulb in the beginning of this activity because it is not
always evident to them that batteries and bulbs have two “ends” (terminals).
At the middle school level, there is one benchmark about constructing circuits and explaining how they
work in terms of the flow of electricity and one about applying knowledge of circuits to electrical devices:
IV.1.MS.5 Construct simple circuits and explain how they work in terms of the flow of current.
Key concepts and tools: Complete circuit, incomplete circuit, short circuit, current, conductors, nonconductors, batteries, household current, bulbs, bells, motors, electrical switches.
Real-world contexts: Household wiring, electrical conductivity testing, electric appliances.
IV.1.MS.6 Investigate electrical devices and explain how they work, using instructions and appropriate
safety precautions.
Key concepts: Flow of electricity for energy or information transfer. Safety precautions for using electrical
appliances; grounding. Documentation for toys and appliances—wiring diagrams, written instructions.
(See IV.2 MS.3, transformations of energy.)
Real-world contexts: Situations requiring assembly, use, or repair of electrical toys, radios, or simple
appliances, such as replacing batteries and bulbs; connecting electrical appliances, such as stereo systems,
TV’s and videocassette recorders, computers and computer components.
IV.2.MS.4 Describe common energy transformations in everyday situations.
Key concepts: Forms of energy, including mechanical, heat, sound, light, electrical, magnetic, chemical,
food energy. See PME-IV.1 m.5 (electricity in circuits), PCM-IV.2 m.1 (energy in changes of state). Total
amount of energy remains constant in all transformations.
Real-world contexts: Motors, generators, power plants, light bulbs, appliances, cars, radios, TV’s,
walking, playing a musical instrument, cooking food, batteries, body heat, photosynthesis (see LO-III.2
m.3, LEC-III.5 m.2).
The explanation presented above, about the loop carrying electricity, can be told to elementary students, but
middle school students are held responsible for understanding and using this explanation (elementary
students only need to know how to wire simple circuits). Middle school students can and should do these
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Learning About Electricity
first activities to refresh their understanding of complete circuits. Then they should discuss and figure out
how electricity makes the bulb light: why a complete circuit is needed, how electricity moves through the
circuit, what the battery does, etc. Any of these questions are good for bringing out students’ thinking.
An acceptable scientific explanation of electrical circuits would be built on this kind of reasoning:
1. Since a complete loop is needed for electricity to flow from the battery, it appears that it goes out one end
of the battery, through the wires and the circuit components (lights, bells, motors, etc.) and back in the other
end of the battery.
An alternative idea (misconception) that students often suggest is that “positive electricity” goes out the
positive end of the battery and “negative electricity” goes out the negative end, combining to light the bulb,
power the motor, ring the bell, etc. A way to test (and disprove) this idea is to try to make a light bulb work
by wiring one end of one battery to the bulb, and the other end of another battery to the other terminal of the
bulb. It won’t work… but let students find this out themselves if this misconception comes up. The fact that
it doesn’t work – but that the circuit only works with one battery attached at both ends – is evidence that
electricity is flowing in one end and out the other.
2. Since electrical energy is converted to light energy (or sound energy, or energy of motion in a motor), the
battery must supply the electrical energy. Additional reasoning about batteries supports this: batteries “wear
out” after awhile, and either must be replaced or recharged – that is, the energy they store is all converted to
other forms in the circuit. Also, students should have seen that two batteries wired in the same circuit with
the same bulb produce a brighter light, showing that each battery has its own supply of energy (represented
by the voltage of the battery – two 1.5 volt batteries wired together end to end create a 3 volt power source).
3. Putting the ideas in 1 and 2 together, it seems reasonable that electricity carries energy around the circuit,
giving it up in conversions to light, heat, motion, sound, etc., and returning to the battery to pick up new
energy.
This is the type of explanation that middle school students should be able to develop, at least with your help.
One caution: While it is tempting to think of electrons flowing around the circuit carrying the electrical
energy, in fact electrons only move at about 1 cm per second, where electricity flows through the circuit from
a battery to the bulb almost instantaneously as the switch is thrown. Electricity is a movement of energy from
electron to electron, similar to how sound travels in air from molecule to molecule, or how dominoes create a
fast-moving trail as they fall into each other.
MI-CLiMB has an inaccurate explanation of electrical circuits. They say “In order for this movement to occur, the path
or circuit must be closed and complete, which allows the energy to flow back to the original power source.” Energy
does not flow back to the original power source. Instead, energy is transformed in the bulb or motor, changing from
electrical energy to light or motion – and heat. It is the electrical charges – which now carry less energy – that must
return to the battery in order for the battery to work. Electrical circuits do transfer energy from the battery to the bulb or
motor, as MI-CLiMB goes on to say, but all of the energy does not return to the battery. The battery is a chemical
device that transforms stored chemical energy to electrical energy. As the chemical reaction proceeds, the products of
the reaction have less chemical energy than the reactants did, as some is transformed into electrical energy, to be used
in the circuit.
Middle school benchmarks also include making and using electromagnets:
Use electric currents to create magnetic fields, and explain applications of this principle. Key concepts: Electric
current, magnetic poles, magnetic fields. (See PME-IV.1 m.5, electric circuits.) Tools: Magnetic compass, battery, wire.
Real-world contexts: Electromagnets, bells, speakers, motors, magnetic switches, Earth’s magnetic field.
Activities 1 and 2 are for elementary grades, 3 through 5 are for middle school, although middle school
students who have not done activities 1 and 2 should before they do 3 through5.
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Learning About Electricity
Activity 1 and Extensions
Focus Question: How can you attach a battery to a bulb to make it light up?
Equipment: Bulbs and bulb holders, batteries and battery holders, wires with alligator clips, paper or
Science Journal for recording experimental set-ups
Instructions for Students:
1. Examine your battery carefully. Make a drawing in your journal, showing the parts you think will be
important for making a bulb light.
2. Examine your bulb and bulb holder. Make a careful drawing of both the bulb and the bulb holder, showing
all the parts you can see.
3. Screw your bulb into the bulb holder. Then, in your team, use the battery and any wires to make the bulb
light. Draw every set-up you try. Indicate which one(s) make the light go on.
4. Draw Conclusions: Why do you think some circuits work, but not others? Where does the electricity go in
the circuits that work?
5. Communicate your results: Make a report that shows one drawing of a circuit that works, and a brief
written explanation of how a circuit has to be attached in order for it to work.
Extension 1-1: Try this activity with buzzers, motors, or other electrical devices in place of the light bulbs.
You have to apply your understanding of electrical circuits to make the buzzer/motor work.
Extension 1-2: Use your creativity to make circuits that consist of two bulbs, or a bulb and a buzzer. This
shows whether you understand the idea of a “complete loop.”
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Learning About Electricity
Activity 2 and Extensions
Focus Question: How can you add a switch into the circuit to be able to turn on and off the bulb?
Equipment: Bulbs and bulb holders, batteries and battery holders, wires with alligator clips, switches
Instructions for Students:
1. Attach a switch in your circuit so that opening and closing it turns on and off the light bulb.
2. Write an explanation in your journal about how the switch works to turn off or on the light.
Extension 2-1: If students ask why some flashlights use two batteries, you could have them try to wire a
circuit with two batteries. They should predict what might happen when two are used instead of one.
Extension 2-2: Take apart a flashlight and try to figure out where the complete loop is that makes the
flashlight work. Make a drawing of the circuit that is used in the flashlight, including the switch.
Electric safety: To review safety rules when using electricity, go to this website:
http://www.miamisci.org/af/sln/frankenstein/safety.html. It has a great simulation of “things not to do” when
using electricity.
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Learning About Electricity
Teacher Notes for Activities 1 and 2: Students’ explanations should include the idea that the complete loop
is broken by the switch, so no electricity can flow to the bulb.) This is a good embedded assessment item to
determine whether they understand that electricity has to flow through a complete loop in order for the
electric device to work. (The reason this extension
activity is not optional is that the word “switch” is in the
key concepts of the benchmark, which means that
students need to understand what one is and how it
works.)
For the extension, if they use the same bulb as with one
battery, the two batteries will produce a brighter light.
Usually two batteries are used in a flashlight to prolong
the time between changing batteries – a different bulb is
used that will be the same brightness, making the batteries last longer. This might be a good way to discuss
electrical energy with students: Two batteries provide more electrical energy for making the bulb light (or the
buzzer sound, or the motor spin), so it either is brighter or lasts longer. The light given off by a bulb is a form
of energy, as are the sounds produced by a buzzer or the motion produced by the motor, as listed in the
elementary benchmark about energy (see first page).
A note about the elementary energy benchmark: Energy is a difficult concept at any age. This
elementary benchmark only asks students to recognize that sound, light and heat are forms of energy, as
are electricity and motion. There are two ways of explaining this to elementary students. One is that none
of these things (light, heat, sound etc.) has any substance to it – they are not made of anything. The other
is that all of them can make you react – a loud sound can make you jump, a bright light can make you
squint your eyes, a lot of heat will hurt, as will a lot of electricity, and a ball rolling into you might knock
you over. Physicists say that energy is “the ability to do work.” That is, it can move you in someway. But
elementary students don’t need to master this definition. All they need to do is recognize that these things
(light, sound, etc.) are forms of energy, not matter. A simple activity for this benchmark is to have
students categorize various appliances, toys, and situations by the type of energy involved (toasters,
ovens, irons etc. produce or use heat; bells, whistles, horns, musical instruments produce sound; etc.)
This benchmark should be reinforced in other science units on sound, light, and force and motion.
For extension 2-2: The circuit in a flashlight usually consists of two batteries, a switch and a bulb. The bulb
is pressed directly against the positive terminal of one battery, so no wire is needed for that part of the circuit.
Usually a piece of metal runs from the other terminal of the battery – at the bottom of the flashlight – to the
switch, and then to the outer rim of the bulb. Sometimes the metal is in contact with the bulb holder, which is
also in contact with the side of the bulb, making a path for electricity to flow.
If students are having a hard time understanding the idea of a complete loop, you can use the following
activity to help them think about electricity flowing through wires. It’s also fun!
Provide each group of 2 or 3 students with a “mystery board.” Tell them that some of the metal knobs on the
front of the board may be connected to each other with wires on the inside. They cannot open the board to
find out which are connected. They have to develop a method for determining which are connected (a
battery, bulb and several wires can be used so that when two knobs are touched with two wires, if they are
connected, they light up the battery – a simple “circuit tester.”) After determining the method and applying it
to the problem, they should write up and present their results. Allow students to puzzle about how to do this,
rather than telling them how to make the circuit tester.
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Learning About Electricity
Assessing Elementary Students’ Understanding
Many elementary students who successfully wire a simple circuit and talk about a “complete loop” still don’t
understand that electricity flows out one end of the battery, through the circuit, and back into the other end. If
you ask students why two wires are needed to make a circuit work, many reply with the typical
misconception that “positive electricity” flows from one end of the battery to the bulb and “negative
electricity” flows from the other end of the battery to the bulb.
Straightening out this misconception is beyond the scope of the elementary benchmark. The corresponding
middle school benchmark introduces the idea of current in a wire. So asking students a question such as
“Why is a complete loop needed to make a bulb work” might elicit either the scientific idea that electricity
needs to flow out one end of the battery and back in the other, or the misconception stated above. At the
elementary level, the complete loop is a conclusion drawn from experimenting. Students don’t need to know
why.
But you can assess their understanding of the complete loop in many ways. Some ways have been suggested
in the extensions. You can ask them to think about how a light switch in your house must work – it
disconnects part of the circuit so that electricity cannot get to the light bulb.
Also you can show them several drawings of circuits that work or that don’t work, and ask them to predict
which would work. They should explain where the complete loop is. For example, of the two drawings
below, only the one on the left would work because there is not a complete loop through the bulb.
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Learning About Electricity
Activity 3
Focus Question: How can you explain why a circuit needs a complete loop?
Equipment: Bulbs and bulb holders (or other circuit devices like buzzers, bells, motors/fans), batteries and
battery holders, wires with alligator clips. You will also need a Science Journal to write notes, make
drawings, record results, etc.
Instructions for Students:
1. Using wires, a battery and a bulb, put together a circuit that works.
2. In your journal, make a drawing of your circuit, showing exactly how the
wires are attached to the battery and bulb. Look carefully at the bulb and bulb
holder to understand how electricity flows through the bulb. Also indicate the
positive and negative terminals of the battery.
3. Discuss with your team why a circuit won’t work if only one wire is
connected from the battery to the bulb. Write your ideas in your journal.
metal sides
4. Think about this analogy: Hot water is sometimes used to heat houses. It gets
Base is insulated
heated by a boiler, then pumped through pipes into every room of the house.
from sides
Then it goes back to the boiler. Often just one pipe carries the hot water
throughout the house, heating every room. Unless there is a leak in the pipes, water never needs to be
added to the pipes.
hot water
boiler and pump
radiator
a. Why does the water return to the boiler?
b. What does the hot water “leave” in every room?
c. How is this analogy similar to the electric circuit you set up?
5. Think about transformations of energy in the house and in your circuit.
a. What form of energy is involved in heating the house? What is the source of that energy?
b. What forms of energy are involved in the electrical circuit? Name as many as you can see, hear or
feel.
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Learning About Electricity
c. Where does the light energy come from that radiates from the light bulb?
d. If the heating system in a house is a good analogy for an electrical circuit, what does the boiler
and pump compare to in the circuit?
e. How is electricity like hot water?
6. If you wired two batteries together in this circuit (instead of one), what would happen to the light from
the bulb? Make a prediction and write it in your journal. Then try it and see if your prediction is
confirmed.
a. What does this tell you about energy in an electrical circuit?
b. Why do both batteries have to be pointing in the same direction in order to work?
7. What would happen to the light from the bulbs if you wired another bulb in the circuit, in such a way
that electricity went through one bulb first and then the other? Make a prediction and write it in your
journal. Then try it and see if your prediction is confirmed.
What does this tell you about energy in an electrical circuit?
8. What would happen to your new circuit (with two light bulbs) if one of the light bulbs burned out?
Hint: Think about what happens inside a light bulb when it burns out. Look at the drawing above to figure
this out. Then you can answer what would happen with the other light bulb.
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Learning About Electricity
How electrical circuits work
Scientists and electricians talk about electrical
charges moving through a circuit. They can only
move through the circuit if the circuit is complete,
because when they are pushed out of one end of
the battery, they need to be replaced in the other
end of the battery. That’s the way the chemical
reaction in the battery works – it needs a constant
flow of charges into one end, in order to push
them out the other end.
They call the flow of charges “current.” They
measure current in amperes, or just “amps” for
short. Fuses in cars and circuit breakers in houses
are rated by how many amps of current they can
handle before they blow. If too much current is in
a circuit, it might overheat the wires, causing a
fire. The fuse breaks first, causing an incomplete
circuit, so no more electricity can flow and the
wires won’t overheat.
 Current is moving charges.
 A complete circuit is needed because the
charges have to return to the battery.
The current carries the electrical energy to the
devices in the circuit. The battery “gives a boost”
to the charges that come in one end, giving them
more energy. When they flow through lights,
bells, motors, etc. some of the energy they carry is
converted into light, sound, heat, or energy of
motion. The amount of push that a battery can
give is measured in volts.
Electrical circuits are wonderful ways of
transferring energy from place to place, making
all kinds of electrical appliances possible. Think
of all the things we would not have without
electricity.
 Current carries electrical energy through
circuits.
 Energy transformations occur in electrical
circuits to produce light, heat, sound and
motion.
There is a great little animation on the web of an
electric circuit, illustrating how a battery gives a
boost to charges moving around a circle, and how
each component in the circuit uses the energy. Go
to
http://www.sciencejoywagon.com/physicszone/les
son/07electr/electri/simplcir/default.html which
shows one component (light bulb, motor, bell,
etc.). They have another animation of two circuit
components at
http://www.sciencejoywagon.com/physicszone/les
son/07electr/electri/sercir/series.html. The text for
this second animation is about series circuits,
which just means a circuit with more than one
component, wired so that electricity passes
through one at a time.
Another type of circuit that is often used in homes
is called a parallel circuit, where two wires come
out of the positive end of the battery and go to one
side of two light bulbs, then wires go from both
light bulbs back to the negative end of the battery.
This has the advantage that when one light bulb
goes out, the other one doesn’t go out too. There
is an animation about parallel circuits on this
website (the main URL is
http://www.cyberclassrooms.net/~pschweiger/dcci
rcuits.html), but you don’t have to learn to
distinguish between series and parallel circuits.
Conductors, insulators and short circuits
What would happen if you tried to use a piece of
string in a circuit, in place of the wire? It wouldn’t
work, of course, because string is not a conductor
of electricity. Metals are good conductors of
electricity, because charges can flow in them
easily. A string, or any other materials that does
not conduct electricity, is called an insulator or
non-conductor. The coating around a wire is an
insulator, so that the electricity does not flow to
any other object that the wire touches.
If the coating on a wire is rubbed off by mistake,
and the exposed wire touches something metal,
the electricity flows out of the wire into what it
touches, creating a “short circuit.” The electricity
goes where it is not supposed to go. Sometimes
you see sparks when this happens, because the
electricity can jump a short distance through the
air.
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Learning About Electricity
Batteries
The electrical energy supplied by a battery is also
the result of a transformation of energy. Chemical
reactions in the battery begin when a complete
circuit is attached to the battery. The substances in
the battery store chemical energy, which is
transformed into electrical energy when the
battery operates. The chemical reaction inside the
battery produces new substances which store less
energy than the original substances, giving up that
energy into the circuit. The battery “wears down”
eventually because the chemical energy stored in
the battery is used up.
The force that batteries exert on charges is called
voltage. Most “flashlight” batteries are 1.5 volts.
If you connect two of them in series (positive to
negative) they combine their push on charges to
make 3 volts. The current in the circuit can carry
more energy, and therefore the light bulb is
brighter with two batteries. You can also make a
flashlight (with a different kind of bulb) that is the
same brightness, but the batteries last longer,
since there is more energy stored in two of them
than in one.
You can take apart a 9 volt battery (used in smoke
alarms and some radios) and see that they are
really just 6 – 1.5 volt batteries wired end to end.
Household current
The electricity that comes from plugs in your
house is 115 volts. Ouch! This electricity comes
from power lines that connect your house to a
power generating plant. Usually the power plants
run on coal, sometimes on natural gas. There are a
few nuclear power plants in use in the U.S., and,
in those places of the country with large, fastrunning rivers, there are power plants that work
from water-driven turbines (hydroelectric plants).
There are even a few wind-powered generators!
Each of these power plants converts the energy in
coal, natural gas, uranium, flowing water or wind
to electricity. It travels through wires (conductors)
to your house, where it powers electrical
appliances. What happens in the electrical
appliance? Another energy conversion! Try to
name a few electrical appliances and the kind of
energy conversions that occur in them.
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Learning About Electricity
Activity 4
Focus Question: How do electrical devices work?
Equipment: VCR, TV, audio components, DVD player, etc. and wires needed to connect them. Electrical
kitchen appliances such as toasters, electric mixers, food processors, etc. A hair dryer to take apart;
screwdriver to take apart hair dryer. Science Journal.
Instructions for Students:
There are two major types of electrical devices. One works with just electricity, transforming it into useful
types of energy. A toasters is an example. It transforms electrical energy into heat energy, to make crisp,
brown bread.
The other works with information that is carried by electrical circuits – information such as voice
communications on phones, digital information on the internet, audio and video entertainment on CD’s,
DVD’s, or cable television.
In “low tech” appliances, the energy conversion is the end product.
In “high tech” appliances, the information carried by the current is the end product. Energy transformations
occur (mostly to light and sound in computer monitors, radios and TV’s) but the content of the light and
sound are what’s important.
1. Label each device as working to A – process information or B – produce useful work. For those devices
that transform energy, indicate the kind of energy that does the useful work in the appliance. For example, in
a toaster, heat energy does the useful work.
A – Process
information
B – Produce
useful work
B – What kind of useful energy?
hair dryer
refrigerator
computer
fan
VCR
digital watch
flashlight
washing machine
garage door opener
CD player
television
electric lawnmower
electric toothbrush
power tools
radio
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Learning About Electricity
2. For this activity you will use a hair dryer. It is very important NEVER to plug the hair dryer into the
wall socket when it is taken apart. You could touch any of the components by mistake and possibly get
electrocuted!
Take apart a hair dryer (make sure it is unplugged during the entire time it is taken apart).
To take apart a hair dryer, first make sure it is not plugged in. Then unscrew the screws that hold the two
pieces of the plastic cover together. Put the screws in a container or other safe place. Do not separate the
wires from the components, but simply pull the components away from each other and away from the two
halves of the cover.
Examine the parts. Consider how a hair dryer works and what each of its functions are.
 Identify its major components.
 Describe the purpose of each component.
 Explain where each of the energy conversions takes place.
 Draw a diagram of a hair dryer, showing how electricity might be wired to each of its components.
There’s a nice photo of a taken-apart hair dryer at http://www.howstuffworks.com/hair-dryer3.htm. You can
see where the exposed wires are connected to the heating element – if you touched those screws while the
hair dryer was plugged in, you could be killed.
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Learning About Electricity
3. Now consider a television set and VCR. They
are plugged into the wall, of course, and they do
convert electricity into motion (to drive the
videotape), light (the picture from the TV) and
sound. But not simple sound, like a doorbell. And
not simple light, like from a flashlight. Instead,
the light and sound have complex information
contained in them.
Instead of following the electricity and
determining the energy conversions, we need to
follow the information, in order to understand
how the components work together.
Step 1: How does the information enter your
house?
There are three ways that information can enter
your house. One is through a cable. This can be a
television cable or a telephone wire.
Another is through radio
waves. Radios pick up
signals that are
broadcast from radio
towers. Cell phones pick
up signals that are
broadcast (and they send
back signals to the cell
phone towers).
Televisions can pick up TV broadcasts through
their antennas.
And the third is when you carry a CD, DVD,
videotape or other recorded medium into your
house.
Step 2: How does a device display the
information?
The information contained in the cable or
broadcast signal, or on the recorded medium, is in
an electronic code. In the cable TV, standard
telephone signal, or internet connection (by
phone, cable modem or DSL phone line) the
electricity itself is coded. That is, electricity flows
through the cable or telephone wire (a lower
voltage than house current), and the electricity is
coded to contain the information. It has to be
decoded by the TV, VCR, telephone or computer
and converted back into meaningful images (light)
and meaningful noises (words, music, other
sounds).
With a cell phone, TV broadcast, AM or FM radio
or satellite TV, the radio signal is coded. Again,
the cell phone, TV or radio decodes the signal that
is “carried” on top of the radio frequency. The
decoded information contains the picture, music,
or phone conversation.
In the case of internet connections and phone
conversations, information goes two ways – into
your device (phone, computer) and back out again
to another phone or another computer. The words
you say go out over a radio signal to the cell
phone tower and are relayed to the other phone.
With the internet, when you type a website
address into your browser and hit “return,” the
address is sent to another computer and relayed on
to the computer that stores those web pages. As
you interact with the web page, the signals race
back and forth.
CD’s, DVD’s and videotapes are different. They
don’t use electricity or radio signals to carry
information. Instead, the information is coded by
lasers (CD’s and DVD’s) or electromagnets
(videotape) into the plastic of the CD or the
magnetic material of the tape.
How are VCR’s, stereo systems and TV hooked
together to record and playback information?
I) Wire a VCR and TV together so that you can
play videos. Make a diagram of how the wires
connect the two devices together, labeling your
diagram with the names of the connectors (the
plugs, or jacks – they are called “ports” on
computers) on the VCR and TV.
 Does information flow from the TV to the VCR
or from the VCR to the TV? How do you know
this?
 What is the purpose or function of the
“TV/VCR” switch?
 How do the names of the connectors tell you
about the flow of information?
Connectors on TV’s and VCR’s (or DVD’s) have
names like “audio in,” “video in,” “video out,”
“antenna in,” etc. There are often different
connectors for video (picture) and audio (sound).
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Learning About Electricity
Sometimes there are several choices for video
signals, depending on the kind of connecting
cables you have and the capabilities of the TV.
You have to figure out what plugs into what by
looking at the kind of connectors you have and
deciphering the labels on the VCR or TV. “Video
In” means that the picture is going into the TV at
that connector. “Video Out” means that the
picture is going out of the VCR through that
connector. What you have to realize, of course, is
that the information is stored on the videotape and
has to make its way to the TV through the wires.
II) Wire a VCR and TV together with a cable
or antenna (satellite or broadcast) so that you
can record one program while watching
another. Do this by thinking about how the
information has to flow – where it starts, where it
has to go. Make hypotheses within your group,
test your hypotheses, and see what works.
The “TV/VCR” switch is a critical element in this
set up of components. As its name suggests, it
allows either the VCR or the TV to control what
you watch. When the VCR is in control, you can
watch a video or change channels through the
VCR’s tuner (with the TV set to either channel 3
or 4, depending on how you set the “3/4” switch
on the back of the VCR).
With the TV in control, you can change channels
on the TV. In this setting, you cannot watch a
videotape, because information is not coming
from the VCR.
 Once you get it working, make a diagram of
how the wires connect the devices together,
including the names of the connectors. Use arrows
to show the flow of information through the
system.
When you can figure out how to connect a VCR
and TV to tape one show and watch another, you
can figure out how just about any system of
electronic equipment should work together. Just
follow the flow of information!
If you are interested in reading more about other
electronic devices, use How Stuff Works.com.
They have a search box that lets you look up just
about any device. Cell phones, for example, are
written about at
http://www.howstuffworks.com/cell-phone.htm.
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Learning About Electricity
Teacher Notes for Activity 4:
The goal of this activity is for students to figure out how electricity flows in a useful appliance, and what the
energy transformations are the make the appliance useful.
Make sure that students never plug the hair dryer into a wall socket when it is taken apart. There is an
EXTREME ELECTROCUTION HAZARD from opening the hair dryer when the cover is off.
The main components of a hair dryer include the switch, the blower motor and fan, and the heating element.
The blower motor and fan transforms electricity into energy of motion (moving air). The air moves across
the heating element (in which electricity is transformed into heat energy) and gets hot, moving out of the hair
dryer and onto someone’s hair.
The website How Stuff Works.com has an article on hair dryers, which you should use with students. They
show a photo of a taken-apart hair dryer.
The electrical diagram for this appliance should show electricity from the source (wall socket) going through
a switch, then going to both the heating element and the blower motor, then returning to the other side of the
source. There are two ways to draw this, both correct, as shown below, but the second drawing is more
traditional (although harder to grasp at first). The simulation of two light bulbs in a parallel circuit at the
website given on page 10 shows essentially the electrical circuit of a hair dryer, drawn similarly to the second
diagram below. (http://www.sciencejoywagon.com/physicszone/lesson/07electr/electri/parcir/default.htm)
motor
and fan
switch
switch
heater
coil
wall
outlet
motor
and fan
heater
coil
wall
outlet
Many hair dryers use a three-way switch, OFF, LOW and HIGH, which controls the amount of electricity
going to the fan and heater – more on HIGH, less on LOW.
Wiring a VCR and cable TV to record and watch different programs:
Of course, students could follow the wiring diagrams in the instruction booklets. But the inquiry activity
here, and the purpose of the benchmark, is to figure out how the wires must be connected so that the
information flows to the appropriate places.
You can easily do activity I) – wiring a VCR and TV together to play a tape – in the classroom. Activity II)
requires a cable or satellite TV feed, which many classrooms do not have. Enlist the help of your media
specialist or technology specialist to find a location for this activity where all students can participate.
Here’s how the TV/VCR set-up works: The information comes into the house through the cable (for cable
television) or through an antenna wire for satellite T.V. It goes into the VCR, where it is “tuned” by the
controls on the VCR to the channel that you want to tape. You can also watch that channel if you hit the
“TV/VCR” switch so you are viewing the VCR signal (this is, you can set the TV/VCR switch so that the
VCR is in control of what you watch).
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Learning About Electricity
The “video out/audio out” connector (sometimes labeled just “out” or “to TV”) sends a signal from inside the
VCR to the TV. If you don’t want to watch what the VCR is taping, the “TV/VCR” switch – set to TV –
sends the signal from the cable directly to the TV. If you do want to watch what the VCR is taping (or what
has already been recorded on a tape), the “TV/VCR” switch – set to VCR – sends the signal from the VCR
mechanism to the TV.
Student drawings should show how the information flows in this set-up, depending on how the “TV/VCR”
switch is set.
The tuner is the channel controller. For the VCR to play through the TV, the TV is usually set to channel 3 or
4 and left alone. A videotape can play through the TV, or the tuner in the VCR can be set to any channel and
played on the TV.
switch on “TV”
Cable
channel
tuner
channel
tuner
VCR
picture
tube
videotape
recorder
switch on “VCR”
TV
Teacher notes for Activity 5:
A demonstration motor is available from the Jackson County Mathematics and Science Center that shows
how motors work. The speed of the motor can be controlled by changing how often the polarity of the
electromagnets is changed. This demonstration motor used an ingenious design to change the polarity of the
electromagnets.
Answers to questions:
 Look at the drawing. How would you predict that the spinner magnet would move? The north pole of
the electromagnet would repel the north pole of the permanent magnet, and the south poles would repel,
making the bar magnet spin counterclockwise.
 Just when the spinner magnet moves one-half circle, the electromagnets have their polarity changed, so
the one on the left is now N, and the one on the right is not S. Then what would happen to the spinner?
The reversed polarity of the electromagnets would again repel the (changed) polarity of the bar magnet,
continuing the spinning motion.
 How could you change the polarity of the electromagnets? Reverse their connection to the battery that
powers them. Actually, in many motors, AC current (house current) is used (rather than DC current in
batteries), which changes its direction 60 times per second.
 How could the motion of the spinning magnet be continued? Continue to reverse the polarity of the
electromagnets at just the precise time to give the bar magnet a continued push.
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Learning About Electricity
Activity 5
Focus Question: How can you make an electromagnet?
Equipment: Batteries, thin insulated wire, a large iron nail, some metal objects that may be attracted to a
magnet, a compass. Optional: a bar or horseshoe magnet, paper and iron filings.
Instructions for Students:
1. Make an electromagnet by wrapping wire around a nail (at least 50 turns) and attaching it to a battery. Test
it with the compass. Use it to pick up objects.
A nice description of electromagnets and how they work can be found in Marshall Brain’s How Stuff
Works web pages, at http://www.howstuffworks.com/electromagnet.htm. That website includes the
following diagram for making an electromagnet:
Your electromagnet should have at least
50 turns of wire around the nail.
2. What could you do with an electromagnet? How many applications of electromagnets can you think of?
3. How can you make a stronger electromagnet? Think of two different ways you might make a stronger
electromagnet, and try them. How can you measure the strength of your electromagnet?
 Why can a magnet, either a permanent magnet or an electromagnet, pick up an object that it is not
touching? Write your initial ideas in your science journal.
Investigation: See how close you can get your electromagnet to a paper clip before the paper clip starts
to move towards the magnet. Design an experiment to test the strength of an electromagnet using this
procedure. In your write-up of the results, include an explanation of this “action at a distance” effect.
Does it depend on which end of the electromagnet you use? Does it depend on whether you try to attract
the paper clip to the mid-point of the nail? Does it depend on the strength of the nail?
Have you ever placed a piece of paper over
a bar magnet (or a horseshoe magnet) and
sprinkled iron filings on the paper. If you
giggle the paper a little, the filings make a
pattern that is related to the shape of the
magnet (your electromagnet will work for
this, too). Given what you found in your
investigation, what do you think this pattern
shows?
N
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Learning About Electricity
 What do you know about “magnetic poles”? How are they like the Earth’s North Pole and South Pole?
Write what you know about magnetic poles in your journal.
4. Design a tool that could slide 20 feet down into a metal baseboard air duct (galvanized steel, not
aluminum) and retrieve a lost key (also attracted to a magnet).
5. Read the article at http://www.howstuffworks.com/motor.htm about electric motors. Motors are a very
important application of electromagnets. A permanent bar magnet is attached to a spinner, with (obviously)
north on one end and south on the other. Two electromagnets are placed at opposite ends of the spinner, just
a little distance away from the ends of the permanent magnet.
N
N
S
S
spinner
 Look at the drawing. How would you predict that the spinner magnet would move?
 Just when the spinner magnet moves one-half circle, the electromagnets have their polarity changed, so
the one on the left is now N, and the one on the right is not S. Then what would happen to the spinner?
 How could you change the polarity of the electromagnets?
 How could the motion of the spinning magnet be continued?
A motor has a mechanism in it that changes the polarity of the electromagnet at just the right point to keep
the permanent magnet moving. The permanent magnet has an axle through it’s middle, attached to gears that
can be used to drive wheels, fans, drills or anything that needs a motor to run!
You can build your own motor with a kit available at many hobby shops or through science supply
companies.
This website also provides an explanation of how motors work, based on electromagnets:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/mothow.html#c1
Another increasingly important application of electromagnets is in “maglev trains” – trains that levitate
above the tracks on magnetic fields. See the article at http://www.howstuffworks.com/maglev-train.htm.
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Learning About Electricity
Assessing Middle School Students’ Understanding
Most of the problems posed for students in Activity 3 can be used as “embedded assessments.” That is, you
can watch, listen, and ask probing questions of students as they attempt to wire various circuits, and you can
read their journals to assess their understanding.
Along with embedded assessments, the following questions can give you insight into students’
understanding. You might ask them to write out answers individually, or discuss within their groups and
write group reports.
Questions for deliberation:
Why is a complete circuit needed to make an electrical appliance (bulb, buzzer, refrigerator) work?
What happens in a house circuit when you turn on or off a switch? Can you make a diagram to show this?
What moves around a circuit?
What does the battery do in a circuit?
What does the concept of conductivity mean?
What does a switch do in terms of conductivity?
Why does a strand of holiday lights stay on even when one burns out? Can you make a diagram to show this?
Why do scientists say that magnetism and electricity are related?
Also see the unit assessment on electric circuits developed by the Jackson County Mathematics and Science
Center Middle School Assessment Team, available with the Jackson County Model Science Curriculum.
Performance assessment:
A standard performance assessment is to have students wire a model house. This draws on their
understanding of how circuits work, and allows them to use their creativity in the design.
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