Download What is an Electric Circuit?

Unit 2 Investigation 2 Electricity
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What is an Electric Circuit?
Contents
• Introduction
• Thinking About the Question
• Materials
• Safety
• Trial I
• Trial II
• Trial III
• Technical Hints
• Analysis
• Further Investigations
Introduction
Discovery question: What is an electric circuit?
Cartoon:
Thinking About the Question
What is an electric circuit?
Looking at the set-ups below. Which one will light the bulb, A or B? Explain your
answer.
[Answer: A. A does not have a break in the wire so it will light the bulb.]
A.
B.
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A “circuit” is a complete loop of wire that allows electrical charge to flow. When
electric charge flows, it can light a bulb. What would you have to do to set-up “B”
above to make electrical charge flow?
[Answer: Take the break out of the wire to close the circuit.]
Electric circuits can be made in different ways to do many things. In many cases,
things that you use do more than light a single light bulb. Can you think of
something that has more than one lit bulb?
[Answer: Most alarm clocks, an electronic game, some lamps, some flashlights,
most ovens, etc.]
In this Investigation, you will build different types of electric circuits.
Materials

Voltage sensor [linked to technical hint]

2 good AA batteries

2 holiday bulbs with stripped wire ends
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1 medium (1¼”) binder clips
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2 alligator clips
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1 thick rubber band. (About ¼” by 6” in circumference.)
Safety
Use only the batteries described in the materials section. Larger batteries may
heat up the bulbs too much, which could be dangerous. When using the binder
clips, be careful not to pinch your fingers.
Trial 1
Lighting more than one holiday bulb
1. Connect the two AA batteries together using the binder clip as
shown below. The Positive End (marked +) of one battery needs to
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connect to the Negative End (marked -) of the other. Make sure
you push the batteries together so that they are touching each
other.
2. Connect the alligator clips using a rubber band as shown below.
Make sure you have a good connection between the wires and your
batteries.
3. Clip the alligator clips to a bulb.
4. Look at the brightness of the bulb. Using the Drawing Tool, draw
the brightness of the bulb. If it is very bright, draw a lot of light
coming from the bulb. If it is dim, draw only a little light.
[Answer: The bulb will be fairly bright. This is subjective, but meant to
get the student thinking about the brightness.]
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5. If you use two bulbs as shown in the picture below, what do you
think would happen to the brightness of the bulbs? Write what you
think will happen.
[Answer: Student answers will vary.]
6. Add the second bulb and look at the bulb brightness. Using the
Drawing Tool, draw the brightness of the bulbs. If they are very
bright, draw a lot of light coming from the bulbs. If they are dim,
draw only a little light.
[Answer: The bulbs will be less bright than in question 4.]
7. How did the brightness of each of the bulbs in the two bulb circuit
compare with the brightness of the one bulb circuit?
[Answer: The brightness of bulbs in the two bulb circuit was much less
than the brightness of the one bulb circuit.]
Trial 2
A different way of connecting bulbs in a circuit.
1. Two different circuits (labeled A and B) with two lights each are
shown below. Described some differences in the two circuits?
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B
[Answer: Circuit A has two bulbs connected side by side on one loop
of wire. Circuit B has two different looks of wire.]
2. When bulbs are attached all on one loop of wire it is called a
“series” circuit. Circuit A is an example of a series circuit. When
bulbs are connected on separate loops of wire it is called a “parallel
circuit.” Circuit B is an example of a parallel circuit. Which circuit is
like the one you have been using? Why?
[Answer: Circuit A. We have been using a series circuit which has
one loop of wire.]
3. As a class, you are going to compare series circuits with parallel
circuits. Ask your teacher which type of circuit your team should
build and mark the circuit type you are building below.
Our team is building a series circuit
Our team is building a parallel circuit
4. Build your series or parallel circuit as shown in the pictures below.
Series
Parallel
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5. Get together with another team that is building a different type of
circuit. Look at the brightness of the light bulbs in a series circuit
and in a parallel circuit. Are the bulbs in each circuit the same
brightness? If not, which circuit has brighter bulbs?
[Answer: No, they are not the same brightness. The parallel circuit
has brighter light bulbs.]
Trial 3
Measuring Voltage in a Circuit
1. In Investigation 1, we found out that two batteries can make a
single holiday bulb brighter than one battery. This has to do with
voltage, which we can measure with the voltage sensor. Now you
are going to measure voltages in your circuit.
Measuring Voltage in a Parallel Circuit.
2. Using the voltage sensor, measure the voltage across the battery.
Make sure to connect the red wire to the positive (+) side of the
battery as shown. Record the voltage.
Battery Voltage:
[Answer: around 3.0 volts.]
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3. Now measure the voltage across each holiday bulb as shown.
Record the voltages.
Bulb 1
Bulb 1 Voltage:
[Answer: around 3.0 volts.]
Bulb 2 Voltage:
[Answer: around 3.0 volts.]
4. The voltages across the
batteries and the bulbs are
shown below. What do you
notice about the voltages?
Bulb 2
Voltages in a Parallel Circuit
3.0
0
across
batteries
across
bulb 1
across
bulb 2
[Answer: the voltages are very close to one another.]
5. Get together with another team that measured voltage on a
different type of circuit. Does the graph of voltages look the same
for each type of circuit? Explain.
[Answer: No. In the parallel circuit, the voltages the same – the
battery voltage is the same as each bulb voltage. In the series circuit,
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the voltages of the bulbs looks like about have of the voltage of the
battery.]
6. How do the voltages measured compare with the brightness of the
holiday bulbs in series and parallel circuits?
[Answer: the higher the voltage across the bulb, the brighter it is.]
Measuring Voltage in a Series Circuit.
2. Using the voltage sensor, measure the voltage across the battery.
Make sure to connect the red wire to the positive (+) side of the
battery as shown. Record the voltage.
Battery Voltage:
[Answer: around 3.0 volts.]
3. Now measure the voltage across each holiday bulb as shown.
Record the voltages.
Bulb 1 Voltage:
[Answer: around 1.5 volts.]
Bulb 1
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Bulb 2 Voltage:
[Answer: around 1.5 volts.]
Bulb 2
4. The voltages across the batteries and the bulbs are shown below.
What do you notice about the voltages?
Voltages in a Series Circuit
3.0
0
across
batteries
across
bulb 1
across
bulb 2
5. Get together with another team that measured voltage on a
different type of circuit. Does the graph of voltages look the same
for each type of circuit? Explain.
[Answer: No. In the parallel circuit, the voltages the same – the
battery voltage is the same as each bulb voltage. In the series circuit,
the voltages of the bulbs looks like about have of the voltage of the
battery.]
6. How do the voltages measured compare with the brightness of the
holiday bulbs in series and parallel circuits?
[Answer: the higher the voltage across the bulb, the brighter it is.]
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Technical Hints
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
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Setting up a voltage sensor
Using the drawing tool
Recording voltages
Analysis
1. Which of the following circuits will light the holiday bulb or bulbs the
brightest if all the AA batteries are new?
A.
B.
C.
[Answer: C]
2. Use the drawing tool to draw a circuit with 3 bulbs in parallel. Make
sure to include a battery. Refer to Technical Hints to create a
drawing.
[Answer: See drawing below.]
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3. Suppose you had 2 AA batteries and 2 holiday bulbs and you
wanted to make as much light as possible with a circuit. How
would you make your circuit? You can describe with words or use
the drawing tool to make a drawing. Refer to Technical Hints to
create a drawing.
[Answer: connect the batteries in series (3V) and then connect the bulbs in
parallel.]
Further Investigations

Make a circuit that has a switch to turn a light on and off. One way to
make a switch is to make two holes in a piece of cardboard that are the
length of the paper clip apart. Insert a paper fastener through a paper clip
and then through the cardboard. Insert another paper fastener through
the other hole. Wires from your circuit can be connected to the paper
fasteners. A drawing of a switch is shown.

Make a circuit with 2 holiday bulbs in series and measure the voltage of
the battery or batteries. Then measure the voltage across each bulb. Add
another bulb to the circuit so that you have 3 bulbs in series. Measure the
voltage across each bulb. Add another bulb so that you have 4 bulbs in
series. Measure the voltage across each bulb. Record your results in the
table below or with your own table. Do you see any patterns with the
voltage across the bulbs?
battery voltage
2 bulb circuit
bulb 1
3 bulb circuit
bulb 1
4 bulb circuit
bulb 1
bulb 2
bulb 2
bulb 3
bulb 1
bulb 3
bulb 4
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Can you make a circuit that will light a bulb and make a motor run? Can
you think of something that you use at home that lights a bulb and makes
a motor run?