Masks and vaccinations are recommended. Plan your visit
Wind up a coil of wire, attach it to the bottom of a paper cup, hold a magnet nearby, and listen to the radio! You’ve made your own speaker.
Plug the mini phone plug into your radio, phone or other device, then turn it on and play some music (you may have to turn the volume up louder than you normally would). With one hand, hold the cup to your ear. With your other hand, bring a magnet closer and closer to the coil of wire until you can hear the sound produced by your homemade speaker.
If you have two magnets, you can put one inside the bottom of the cup and the other next to the coil, on the outside of the cup (so the two magnets hold each other on) to keep the sound going.
Look down at the loop of wire. When electric current goes around the loop clockwise as you look at the loop, there is a south magnetic pole nearest you. When the current reverses there is a north magnetic pole nearest you.
When the south magnetic pole of a magnet is near the coil of wire it will attract a north pole and repel a south pole of the coil electromagnet. The coil will move toward and away from the magnet, depending on the direction of the electric current. Because the coil is attached to the cup, the cup will also move toward and away from the magnet.
The cup pushes air back and forth, creating a sound that travels to your ear. The bare wire itself does not move much air, so it 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.
Inside almost every speaker there will be a magnet, a coil of wire, and a thin material to convey the sound into the air. The invention of strong rare-earth magnets allows speakers to create more sound using less electric current.
Paper cups make handy speakers because they fit easily over the ear, but you can use just about anything to vibrate the air. Attach the coil to other objects, hold them near your ear, and hear what happens.
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Attribution: Exploratorium Teacher Institute