A device used in electrical circuits to maintain a constant relation between current flow and voltage. Resistors are used to step up or lower the voltage at different points in a circuit and to transform a current signal into a voltage signal or vice versa, among other uses. The electrical behavior of a resistor obeys Ohm's law for a constant resistance; however, some resistors are sensitive to heat, light, or other variables.♦ Variable resistors, or rheostats, have a resistance that may be varied across a certain range, usually by means of a mechanical device that alters the position of one terminal of the resistor along a strip of resistant material. The length of the intervening material determines the resistance. Mechanical variable resistors are also called potentiometers, and are used in the volume knobs of audio equipment and in many other devices. Compare capacitor. See more at Ohm's law.