Rheostat - An introduction

http://encyclopedia2.thefreedictionary.com/Rheostat

Rheostat (rē`əstăt'), device whose resistance to electric current depends on the position of some mechanical element or control in the device. Typically a rheostat consists of a resistance element equipped with two contacts, or terminals, by which it is attached to a circuit: a fixed contact at one end and a sliding contact that can be moved along the resistance element. Electric current enters and leaves the resistance element through the contacts. By moving the sliding contact toward or away from the fixed contact, the length of the resistance element through which the current travels can be decreased or increased. In this way the current through the circuit can be increased or decreased. Rheostats are widely used for such purposes as controlling the speed of electric motors and dimming electric lights, but they have been replaced in many applications by systems based on semiconductor devices that waste far less power

rheostat [ˈriːəˌstæt]

n

(Engineering / Electrical Engineering) a variable resistance, usually consisting of a coil of wire with a terminal at one end and a sliding contact that moves along the coil to tap off the current

rheostatic  adj

http://www.britannica.com/EBchecked/topic/501162/rheostat

Rheostat

rheostat, adjustable resistor used in applications that require the adjustment of current or the varying of resistance in an electric circuit. The rheostat can adjust generator characteristics, dim lights, and start or control the speed of motors. Its resistance element can be a metal wire or ribbon, carbon, or a conducting liquid, depending on the application. For average currents, the metallic type is most common; for very small currents, the carbon type is used; and for large currents the electrolytic type, in which electrodes are placed in a conducting fluid, is most suitable. A special type of rheostat is the potentiometer, an instrument that measures an unknown voltage or potential difference by balancing it, wholly or in part, by a known potential difference. A more common potentiometer is simply a resistor with two fixed terminals and a third terminal connected to a variable contact arm; it is used for such purposes as a volume control in audio equipment.