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The microphone is a device that converts sound waves into electrical signals. Microphones use the generator effect to induce (create) a changing current from the pressure variations of sound waves.

Moving-coil microphones

The diagram shows a moving-coil microphone.

In a moving-coil microphone:

1. pressure variations in sound waves cause the flexible diaphragm to vibrate
2. the vibrations of the diaphragm cause vibrations in the coil
3. the coil moves relative to a permanent magnet, so a potential difference is induced in the coil
4. the coil is part of a complete circuit, so the induced potential difference causes a current in the circuit
5. the changing size and direction of the induced current matches the vibrations of the coil
6. the electrical signals generated match the pressure variations in the sound waves