Rheostat is a type of variable resistor, which is used to control the flow of electric current either by increasing or decreasing the resistance value.
The word rheostat is taken from two Greek words “rheos” and “statis” which means current controlling device. The term rheostat was made by the English scientist Sir Charles Wheatstone.
Construction of Rheostat
The construction of the rheostat and potentiometer is almost similar. Like the potentiometer, the rheostat consists of three terminals with two connections. The structure of the rheostat is shown below:
The three terminals of the rheostat are called terminals A, B, and C. However, use only two terminals either A and B or B and C. In the above figure, two terminals of rheostat A and C are fixed and connected to both ends of the resistive element called track. Terminal B of the rheostat is the moving terminal connected to the sliding wiper or slider. As the wiper moves across the resistance path along the resistive element, the resistance of the rheostat changes. A rheostat’s resistive element consists of a wire loop.
Symbol of Rheostat
Working of Rheostat
A rheostat is based on Ohm’s law that current is inversely proportional to resistance for a given voltage. This means that current decreases as resistance increases and current increases as resistance decreases. A rheostat’s resistance is increased by adding coils of metal wire to increase the length of the circuit. One of the rheostat’s terminals receives the current, which flows through the coil of wire and makes contact before exiting the other end. The rheostat has no polarity and works the same way when the terminals are switched back and forth.
Types of Rheostat
Rheostat has three types which are given below:
- Linear type
- Rotary type
- Preset type
Linear type
It is cylindrical in the form in which wipers or sliders move linearly and has a linear resistive path. These are mainly used in laboratories for teaching and experiments.
Rotary type
It has a rotary resistive path. On this, the wiper or slider is hooked up on a shaft and moved in a rotary manner, rotating over 3⁄4 of a circle. They are mainly used in power applications.
Preset type
These type are small in size and nothing but a small rheostat. Trimmers or preset rheostats are utilized in a printed circuit board for calibration purposes.
Applications of Rheostat
- Generators
- Motor speed control
- Heater and oven temperature control
- Volume control
- Dimmer circuits