Rheostat is an electrical device used in many used in applications that require the adjustment of current or the varying of resistance in an electric circuit. This device was named “Rheostat” using two Greek words “rheos” and “status” (meaning a current controlling device), by an English Scientist Sir Charles.
Rheostats are two-terminal devices, with one lead connected to the wiper and the other lead connected to one end of the resistance track. The rheostat is a type of variable resistor, whose resistance can be changed so as to change the amount of current flowing through a circuit.
Similar to the potentiometer, a rheostat has three terminals, two fixed and one moving. Also, this moving terminal slides over a resistive path. This resistive path can be of any type of resistive material such as carbon composition resistor, wire-wound resistor, conductive plastic resistor and ceramic resistor.
The main three factors on which the resistance of a material depends is its length, area of cross-section and the type.
- The effective length is changed using a sliding contact. A rheostat as already discussed has a fixed and a moving terminal. The effective length is that between the fixed terminal and the position of the sliding terminal on the resistive path. As the slider moves, the effective length changes thereby changing the resistance of the rheostat.
- Since resistance is directly proportional to the length, as the effective length increases, the resistance increases. Similarly, as the effective length decreases, resistance offered by the rheostat decreases.