magnetic fields to work. Microphones do, too. They are constructed like earbuds, but they work in reverse; they convert sound to electrical energy by electromagnetic induction. A microphone has a thin aluminum diaphragm attached to a coil in a magnetic field, as shown in Figure 3. Sound waves cause the diaphragm to vibrate. This moves the attached coil. The motion of the coil in the magnetic field induces an EMF across the coil's ends that generates a current. The induced EMF and current vary as the frequency of the sound varies. In this way, the sound waves are converted to electrical signals. The potential differences generated are small, typically 10 3 V, but they can be increased, or amplified, by electron