(Lansing State Journal, March 3, 1993)
Question submitted by T.J. of Williamston.
Although there are different models of microphones, they all do the same job. They transform acoustical movements (the vibrations of air created by the sound waves) into electrical vibrations. This conversion is relatively direct and the electrical vibration can then be amplified, recorded, or transmitted.
The type of microphone found in most telephones is called the "carbon" microphone. It consists of a thin cylinder filled with grains of charcoal and closed by a membrane. An electric current passes through this cylinder. When a sound wave hits the membrane it compresses the charcoal grains creating a better contact and changing the electrical current.
A dynamic microphone (the type used by many musicians) operates like a miniature electric power generator. An electric vibration is created when a coil of wire moves near a magnet. The motion of the coil is caused by the incoming sound waves. In this way, the dynamic microphonescan also producs sound, only in the reverse direction: They transform electrical vibrations into sound waves.
Science Theatre would like to thank N. Mousseau for contributing to this article.