Chris McGuinness
Oct 26-27, 2010
Electromagnets and Speakers
In this lesson we will teach the students about electromagnetism by making an
electromagnet with a bolt, coil of wire and battery. We will use this to pick up paper
clips, and compare them to permanent magnets. In the second part of the lesson we will
use the magnets to make speakers and play music.
Materials
Part 1
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22 gauge insulated wire (24” long strips)
3” long iron or steel bolts
Batteries (D or 9V??)
Tape and/or alligator clips
Paper clips
Permanent magnets
Part 2
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Permanent magnets
Wire
Cups (paper, styrafoam, large paper bucket, pie tins)
Tape
Radio with connectorized cable
Introduction (5-10min)
Review previous lessons on circuits. Relate the concept of electricity to magnetism and
describe that we will be making magnets using electricity. Describe the junk yard mover
challenge: Move as many paper clips from one bin to another without touching the
paperclips, and using only one transfer. Ask if the students know of anything they use in
daily life that has electromagnets. Speakers?
Electromagnets (20min)
Begin by letting the students try and move paper clips with the ordinary magnets. They
should be able to pick up paper clips with the magnet, but not be able to release the paper
clips without using their hands. This is the difficulty with permanent magnets; they are
permanent. If we want to build a magnet we can turn on and off, we need to use
something else. Electricity.
Now let the students try and move the paper clips with the bolt. This doesn’t work
because the bolt is not a permanent magnet But we can make it magnetic using
electricity. Construct the electromagnet
1. Wrap the wire in a tight, even coil around the bolt. Leave 3 or 4 inches of wire
loose at each end. Keep wrapping the wire until you get to the end of the bolt.
There may be as many as 3 or 4 layers of wire all the way up and down the bolt.
Your electromagnet should look something like this:
2. Attach one end of the wire to the positive (+) end of one of your batteries. Attach
the other end of the wire to the negative end (-) of your battery pack.
3. Try to pick up one of the paper clips with your electromagnet. Now unhook one
of the wires from the battery. Does the electromagnet pick up paper clips now?
Questions:
1. What do you need flowing through the wire to make the iron bolt act like a
magnet? (Current or Electrictiy)
4. How many paper clips will your electromagnet hold? Can you hang clips on both
ends of the bolt?
5. How can you make your electromagnet stronger? Try adding more batteries to
your battery pack. Make sure all the batteries “face” the same direction in the
circuit (in parallel). Now, how many paper clips will your electromagnet hold?
6. Does is help to have more turns with the wire or less? Try adding more turns with
the wire and see how many paper clips you can pick up now.
Speakers (20min)
1. Leaving about 10 centimeters on the end, wrap the wire around a pencil to make a
wire coil and tape or glue it to the bottom of the cup. The coil should be about 1
centimeter in diameter and contain about 15 coils.
2. Strip the insulation off the ends of the wire.
3. Place the magnet on the wire coil.
4. Connect the signal source (tape player).
5. Adjust the apparatus until you get sound coming out of your speaker.
Questions
1. Does the volume control on the tape player work on your speaker?
2. What kind of sound quality do you get out of your speaker? Compare the loudness
and the clarity.
3. How do the different types of cups sound different?
4. How does the sound quality compare with cup-and-string walkie-talkies?