Teaching Notes

When the students hold the magnet to the coil of the earphone, caution them to keep a small space between the two, so the coil, and the bottom of the cup are free to vibrate. You might suggest that they devise a way to mount the magnet in just the right spot (perhaps by taping it to cardboard, and then taping both to the bottom of the cup with the cardboard shimmed out around the outside). You can hook up a speaker that students can touch so they can feel the vibrations when the speaker produces sound.

You may want to set up a station for Steps 8 through 18 (see Advance Preparation and Setup). Groups could go to this station while other groups are working through Steps 1 through 7.

If the students are working around a 110-V incandescent bulb, caution them to leave the bulb in its socket at all times.

Students readily associate sound with vibration for obvious examples like the guitar or the cymbals. You can help them make this association more general by setting up a station where they can feel the vibration of a speaker that is producing a low tone from an audio oscillator (amplified, of course). Then when students hear sound from the earphone they build, you can ask about the source of the vibrations (the back-and-forth movement of the speaker coil).