Some microphones are shown above. The first to the left is a carbon containing microphone from an old telephone. The other two are piezoelectric microphones. These are probably the most commonly used today.
Microphones are used to turn sound into electrical current. A common type of microphone is the piezoelectric microphone. The microphone pickes up vibrations and puts stress and pressure on a crystal. When the crystal bends, it produces an electric potential across certain points of the crystalline structure. This small potential can then be amplified and sent to a speaker, or recorded. This is the same way the pickup on a record player works.
Another type of microphone, which is commonly found in older phones where the microphone part of the handset unscrews, and the disk type thing comes out. This disc contains carbon powder, which two electrodes are in. When vibrations are picked up by the microphone, it compresses the carbon and pushes the carbon against the electrodes. This causes a change in resistance in the microphone.
A speaker may also be used as a microphone. It picks up the vibrations, and causes a coil of wire to move in a magnetic field, and acts as a generator.
Some microphones are shown above. The first to the left is a carbon containing microphone from an old telephone. The other two are piezoelectric microphones. These are probably the most commonly used today.