A coil, a magnet, and thou


Wind a coil, attach it to a piece of cardboard, hold a magnet nearby and drive it with a tape player.
You have made your own speaker.



Sand the enamel off the ends of the magnet wire until it gleams bright copper, sand the last 5 cm (2 inches).

Wind the magnet wire around the battery, leave 10 cm (4") free of the coil at each end.

Wind coils around a D cell battery.

Slide the coil of wire off the battery and then wrap the free ends around the coils to hold them in place.

Slide the coil off the battery, wrap the free ends around the coil a couple of times.

Tape the coils to a piece of cardboard (or Styrofoam.)

Tape the coil to a piece of cardboard.

Plug the mini phono plug into the tape player, CD player or radio.

A mini phono plug the black barrel is pulled back to show the connections of the wires to the terminals inside the plug.

Connect the alligator clips to the coil.

Tape Player connected to speaker via phono plug.

To Do and Notice

Turn on the Tape Player.

Hold the magnets near the coil of wire.
Put your ear near the cardboard.

Notice the sound produced by your homemade speaker.

What's Going On?

When electric current goes around the loop clockwise there is a south magnetic pole nearest you, when the electric current reverses there is a north magnetic pole.

Hold the south magnetic pole of a refrigerator magnet near the coil of wire and it will attract a north pole and repel a south pole of the coil electromagnet.

When the current through the near side of the coil is in the direction of the arrow the coil is an electromagnet with a south pole down. The gray magnet with north pole up attracts this electromagnet.

The coil will move toward and away from the magnet depending on the direction of the electric current. Since the coil is attached to the cardboard the cardboard will also move toward and away from the magnet.

The cardboard will push air back and forth creating sound which will travel through the air to your ear.

The bare wire itself does not move much air, and so does not make much sound, however if the coil is attached to a large low mass material it will vibrate that material, which in turn will vibrate the air, making a louder sound.

You have made a speaker which turns changing electric currents into sound.

Going Further

Try to make the loudest speaker that you can.

Use different amounts of cardboard, and Styrofoam, assembled in different shapes.

Use different magnets, and more coils of wire.

Attach the headphone output of a radio to a dc electric motor.
Hold the motor in your teeth and listen to the music.

Have other people listen to your ears while you do this and they too can hear the sound.

A motor contains coils of wire and magnets just like a speaker. Holding it in your teeth vibrates your skull and ears. So you and others can hear it as sound.


The simplest speaker involves wrapping the coils of wire around your ear, then holding a magnet near your ear. Play a radio into the coil and turn your ear into a speaker.


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Scientific Explorations with Paul Doherty

© 2003

8 March 2003