A rheostat is a device used to change the amount of current flowing through a circuit by changing resistance. The word Rheostat was derived from the Greek words ‘’rheos’’ and ‘’statis’’, which means a current controlling device. It consists of two terminals, a fixed one and a moving one. Some rheostats can even have three terminals like a potentiometer, but mainly only two are used. Only one out of the two fixed terminals and one moving terminal is used.
Unlike potentiometers, rheostats have to carry a significant amount of current. Therefore, wire wound resistors are more commonly used in their construction.
The function of a Rheostat
Two variables determine the amount of current that flows through a circuit. One is the amount of voltage applied, and the other is the total resistance of the electrical circuit. When the resistance of the course is reduced, the amount of current flowing through it will increase. Similarly, the amount of current flowing through the circuit will increase if the resistance is increased.
The primary function of an electrical circuit is to increase or reduce the current flow. The Rheostat does not entirely block the current flow but only reduces it to a certain extent. If you were to stop the current flow completely, then an infinite amount of resistance would be needed. Therefore, it is practically impossible to bring the current flow to zero.
Rheostats are made of nickel-chromium iron alloy, a high resistivity material that is closely wounded over a circular tube. You can find them in both single and double tubes. Insulation is also provided to avoid short-circuiting of turns. Even the tube of rheostats is made up of resistive material like asbestos.
Construction of a Rheostat
The construction of rheostats is similar to that of a potentiometer. Rheostats mostly have two fixed terminals; one is fixed, and the other is moving, but like potentiometers, they can also have three terminals, out of which only two are used. The moving terminal is found to slide over a resistive path. This resistive path can be made of any resistive material such as a wire-wound resistor, carbon composition resistor, ceramic resistor, and conductive plastic resistor. You can choose any resistive material depending upon the application. However, in most applications, rheostats are found to carry a significant amount of current; therefore, in such a situation, a wire-wound resistive path is selected. The resistive way can either be linear or rotatory.
There are two main types of rheostats available based on the geometry of the resistive path: known linear rheostats and rotatory rheostats. Apart from these two rheostats identified by the geometry of rheostats, there is another type known as terminals.
Applications of Rheostats
Rheostats have been widely used in many applications for a long time. Some of the essential applications of rheostats include the following:
- A rheostat is commonly used in high-voltage applications like refrigerators, microwave ovens, fans, power tools, etc.
- They are used to increase and decrease the speed of a specific motor.
- Rheostats help decrease or increase the volume of devices like TVs, radios, etc.
- They are effectively used as etalon resistance in laboratories.
- Rheostats are used for the measurement of resistance with the bridge technique.
- They can also be found in the buttons through which the temperature setting of electric stoves is controlled.
- Rheostats can be commonly found in light switches or dimmer switches to decrease or increase light intensity.
