A potentiometer is used for precise measurements of voltage, and sometimes current. It also can be used as a three-terminal potential (voltage) divider, which is a type of rheostat. Nearly every type of electronic instrument uses a potentiometer. The most common use is for volume control for radios, televisions and other amplifiers.

Potentiometers make use of rheotats, which are variable resistors. A rheostat is a coil of wire that has been wrapped around an insulating tube and attached to two terminal points. Next to the coil are metal "brushes" that make contact with the coil. When a knob (or "slider") is moved, it causes the position of the brushes on the coil to change, resulting in the resistance between them, and so the terminals of the coil, to change. Heat is produced by resistance, but a rheostat can handle large amounts of current because the coil easily radiates...