Potential difference

The current flowing through a component depends on:

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Potential difference is a measure of the amount of energy transferred between two points in a circuit.

Measuring potential difference

Potential difference is also known as voltage and is measured in volts (V). The potential difference across a component is measured using a voltmeter placed in parallel with the component.

Circuit with a cell, switch and lamp. A voltmeter is connected in parallel with the lamp.

Energy, potential difference and charge

When a charge moves through a potential difference, work is done by the power supply and energy is transferred from it to the component and/or its surroundings. The potential difference can be calculated using the equation:

potential~difference = \frac{work~done}{charge}

This is when:

  • potential difference is measured in volts (V)
  • work done is measured in joules (J)
  • charge is measured in coulombs (C)
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One volt is the potential difference when one coulomb of charge transfers one joule of energy.

Example

2 C of charge transfers 4 J of energy. Calculate the potential difference needed.

potential~difference = \frac{energy~transferred}{charge}

potential~difference = \frac{4}{2}

= 2~V

Question

3 C of charge moves through a potential difference of 6 V. Calculate the energy transferred.

potential~difference = \frac{energy~transferred}{charge}

Rearrange the equation:

energy~transferred = charge \times potential~difference

= 3 \times 6

= 18~J