Download 17B Electromagnets

Electromagnets
Investigation
17B
17B Electromagnets
How are electricity and magnetism related?
Almost every electrical device that creates motion,
such as a motor, uses magnets. Permanent magnets
are not the only type of magnets used in these devices.
Often, electromagnets are used. Electromagnets
create magnetic forces through electric currents. This
investigation will explore the properties of
electromagnets.
A
Materials
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Electric Circuits kit
Electromagnet coil (in kit)
1 permanent magnet (in kit)
Compass (in kit)
1 “D” battery
Electromagnets
1. Attach the coil, battery, and switch in the circuit shown above. Leave the switch open
so no current flows.
2. Place a permanent magnet about 1 centimeter away from the coil. Stand the magnet
up on its end.
3. Close the switch and watch what happens to the magnet. DON’T leave current
running or the coil will overheat. Open the switch after each trial.
4. Turn the permanent magnet around so its other pole faces the coil. Close the switch
and see what happens now.
5. Reverse the wires connecting the battery to the circuit. This makes the electric
current flow the other way. Repeat steps 3 and 4 of experiment with the magnet.
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Investigation
B
17B
Electromagnets
Thinking about what you observed
a.
Write 2–3 sentences that explain what you saw when the switch was closed.
b.
Propose an explanation for why the magnet moved.
c.
When the magnet was reversed, did the force between it and the coil change direction?
How did the force change?
d. When the coil wires were switched, did the force from the coil change direction? How do
you know?
How is a current-carrying coil like a magnet? How is it different? Explain how this shows
that electricity and magnetism are related.
e.
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Electromagnets
C
Investigation
17B
Comparing the electromagnet to a permanent magnet
1. Attach the potentiometer, coil, battery, and switch in the circuit shown in the
diagram. Leave the switch open so no current flows.
2. Set the compass so the needle, ring, and arrow are all aligned with north. Put the coil
about 10 cm from the center of the compass.
3. Place a permanent magnet on the side of the compass opposite the coil. Bring the
magnet close enough to deflect the needle 20 degrees away from north.
4. Close the switch and adjust the potentiometer so the needle returns to north. The coil
should deflect the compass needle back toward north. Reverse the permanent magnet
if the needle moves the wrong way. DON’T leave current running or the coil will
overheat. Open the switch after each trial.
5. Try moving the permanent magnet to different distances and using the potentiometer
to return the compass needle to north with force from the electromagnet.
D
a.
Stop and think
The permanent magnet is pulling the compass needle to the left. The electromagnet is
pulling the needle in the opposite direction, to the right. When the needle returns to
north what can you say about the magnetic forces from the permanent magnet and
electromagnet?
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Investigation
E
17B
Electromagnets
Iron and electromagnets
1. Use the same circuit as for part 3 with one battery, switch, coil and potentiometer.
2. Rotate the compass until the needle and dial are aligned with north. There should be
no magnets nearby, and no current in the coil for this step.
3. Move a permanent magnet close enough to deflect the needle 20 degrees from north.
4. The coil should be 10 cm from the center of the compass (see diagram above).Close
the switch, then use a multimeter to measure and record how much current it takes
for the coil to bring the needle back to north. Adjust the current with the
potentiometer. Once you have recorded the measurement in Table 1, open the switch
to stop the current.
5. Put the steel pin in the coil so its head is against the coil and 10 cm from the center of
the compass.
6. Adjust the distance of the permanent magnet so the compass needle is deflected
20 degrees from north, like you did in step 3. There should be no current in the coil
for this step.
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Electromagnets
Investigation
17B
7. Close the switch, then use a multimeter to measure and record the current it takes to
return the needle to north with the steel pin in the coil.
Table 1: Electromagnet current with and without the steel pin
Current with bare coil
F
Current with steel pin
Difference in
current
Percent
difference
Thinking about what you observed
How did the steel pin affect the magnetic force created by the coil? Was the magnetic force
reduced, increased, or did it stay about the same? Use your observations to support your
answer.
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