Rheostat, << REE uh stat, >> is a device that can change the amount of resistance in an electric circuit. The design of a simple rheostat is based on three principles: (1) Any electrical conductor—even a copper wire—provides some resistance to the flow of electric current; (2) some conductors, such as a wire made of an alloy (metal mixture) of nickel and chromium, provide a large amount of resistance; and (3) the amount of resistance depends on the length of wire through which the current flows.
In a simple rheostat, a sliding contact made of metal is mounted so that it can slide along a length of resistance wire (a conducting wire that has a high resistance). Current enters the rheostat at one end of the resistance wire, passes through that wire to the sliding metal contact, and then flows through the contact out of the rheostat. Sliding the contact changes the length of resistance wire through which the current flows, and thus changes the amount of resistance in the circuit.
See also Electric circuit (Circuit mathematics) ; Wheatstone, Sir Charles .
