GCSE Physics (AQA)

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Calculating Efficiency

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Energy Conservation and dissipation of energy

Calculating Efficiency

4:21 Energy Calculations
Spec 4.1.2.2
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  • Efficiency of energy transfer is calculated by dividing total useful output energy by total input energy.
  • Efficiency represents the proportion of input energy that becomes useful output energy.
  • Sankey diagrams help visualize energy distribution, showing total input energy, useful output energy, and wasted energy.
  • Both total useful output energy and total input energy are measured in joules, resulting in efficiency having no units.
  • Efficiency can be expressed as a percentage by multiplying by 100.
  • Example: An oven uses 80 kilojoules of electrical energy to provide 30 kilojoules of thermal energy, resulting in an efficiency of 37.5%.
  • Efficiency can also be calculated using power by dividing total useful output power by total input power.
  • In continuous processes, the rate of useful and wasted energy output remains constant, allowing efficiency to be described in terms of power.
  • Both useful output and total input power are measured in watts, with efficiency having no units but can be expressed as a percentage.
  • Example: A low energy light bulb with 65% efficiency and 12 watts input power has a light energy output power of 7.8 watts.

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