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A potential divider is a very simple circuit that allows us to create a certain voltage.

The voltage produced (V) is a fraction of the supply voltage (Vs).

This circuit is a basic building block for many circuits so is therefore very important.

In the exam you may be asked to work out the output voltage (V) when given two resistor values. They are usually found as part of comparator circuits.

To calculate the output voltage you need to use the equation below. In an exam you will be given this though...
      R2
   R1 + R2
x Vs
V =
V
R1 = 100R
R2 = 100R
Vs = 9V
x Vs
x 9
V = 4.5V
V
R1
R2
Vs
Potential Dividers

Potential Divider Circuit

      R2
   R1 + R2
x Vs
V =
      100,000
   100,000 + 50,000
x 12
V =
Vs = 8V
      100,000
        150,000
x 12
V =
Example no.2
A potentiometer is just like an adjustable potential divider. When the shaft is rotated the position of the wiper is moved along the resistive carbon track.

The voltage at the output (on the middle pin) depends on the position of the shaft.

In some potentiometers the wiper is connected to a control knob. In another type, called preset potentiometer, the wiper is adjusted with a screwdriver.

A volume control on a stereo is a potentiometer.

The circuit below shows how rotating the knob on a potentiometer effects the output voltage.
Potential Dividers
A preset potentiometer
A Potentiometer
Circuit symbol
Vs
V
Potentiometer Circuit Diagram

Potentiometer control knob

Potentiometer