A rheostat is an electrical device used in many applications that require the adjustment of current or the varying 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 variable resistor whose resistance can be changed to change the current flowing amount 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 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 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 between the fixed terminal and the sliding terminal’s position 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.
Application of Rheostat
- Rheostats are used for increasing otherwise decreasing a radio volume and amplifying or reducing the electric motor’s speed of an electric motor.
- It is used where high current otherwise high voltage is necessary.
- In power control applications, they are replaced with switching electronics.