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Resistance: A friendly foe

• A variable resistance is one whose value can be varied. In some places in an electronic circuit, we have to put such resistance so that we can vary the amount of current flowing in the circuit. A variable resistance allows more control over current in a circuit.
• Variable Resistance is used as volume control of a transistor, brightness control, contrast control of a T.V or speed control of fan.
• It consists of a track made up of resistive material, which provides resistance path and a wiper which moves on the track thus varying the resistance in the circuit.
• It is a three pin component. Two pins are connected to both the ends of the track. The third pin is connected to a wiper that moves on the track. The motion of the wiper through the track helps in the change of resistance.
• Its value is written on its body. If there is variable resistance of 500kΩ, it means the resistance between its first and third pin is 500kΩ. There is a carbon track between pin 1 and 3 and a conducting metal arm connected to pin 2 moves in between 1 and 3. So on moving pin no 2, resistance varies from 1Ω to 500KΩ.
• There are three types of Variable resistance: Potentiometer, Rheostat and presets. Potentiometer and Preset are the once used in electronic circuits.
• In potentiometer, a plastic or iron shaft is connected to pin 2. By moving the shaft, we can easily change the resistance.
• Preset does not have a plastic or iron shaft connected to the wiper. By moving the track using screw driver we can vary the resistance in pre set.

Symbol of variable Resistance

**Diagrams: Vandana Razdan