Basics of Potentiometer

A potentiometer is three terminal resistor which provides variable resistance at its output.

A potentiometer contains three parts.
  1. Base
  2. Output terminals (3 in number)
  3. Rotating knob
The upper terminal is powered from the input source. The lower terminal connects to ground and output is variable resistance is achieved through lower two terminals.

The variable resistance of a potentiometer is used for two purposes:
  1. To achieve a variable voltage (Potentiometer configuration)
  2. To achieve a variable current in the circuit (Rheostat configuration)

Potentiometer Configuration

A potentiometer configuration utilizes three terminals of the device. Input is applied to terminal 'a', 'c' is ground. Variable voltage output is taken from 'b' and 'c'. The circuit  configuration is shown below:
potentiometer-to-acheive-variable-voltage

Rheostat Configuration

The rheostat configuration uses two terminals. The variable resistors connect in series to the circuit and its knob is rotated for achieving a variable resistance. Since, the variable resistance is in series now, changing its value impacts the overall resistance of the circuit. As per Ohm's law, the resistance is now varied for changing the amount of current, and the overall configuration is named as Rheostat configuration.
rheostat-configuration

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