A microphone converts pressure variations in the air into electrical signals.
Moving Coil Microphones
Moving coil microphones use the inductive properties of a coil of wire moving through a magnetic field.
Ribbon Microphones
Ribbon microphones are much the same but use a thin, electrically conductive ribbon instead of a coil.
Condenser Microphones
Condenser microphones, also called capacitor microphones, use a capacitive capsule.