Variable Resistors

Variable resistors are called potentiometers. There is a fixed value of resistance between two terminals. The moving part of the potentiometer is called the wiper.

Variable resistors are usually a stubby cylindrical shape with a rod poking out one end and with three metals ‘tags’. Figure 2.4 illustrates a typical example. Two of the tags are connected to a horseshoe-shaped resistor fitted inside the cylinder. Hence the resistance between these two tags has a fixed value. The third tag (usually the middle one) is connected to a metal ‘finger’ or ‘wiper’ which is pressed against the side of the curved resistor. When we twist the rod we can move this wiper along the resistor, shifting it away from one end and towards the other. As a result, the resistance between this tag and the ones at the ends goes up and down as we rotate the rod. In the diagram shown below, the horseshoe shape of resistive material is coloured orange, and the wiper is coloured blue.

variable resistor

Variable resistor symbol:

variable resistor symbol.JPG

 

for variable resistor learning activity:

variable resistor.JPG

Variable resistors are of three types:

  1. Carbon Composition variable resistor
  2. Wire wound variable resistor
  3. Cerment type variable resistor

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