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GCSE Physics · key term
The fraction of the total energy transferred that is transferred usefully.
Used by AQA, Edexcel and OCR
Specification 4.1.2.2, 4.2.4.3 · Paper 1
The fraction of the total input energy or power that is transferred usefully.
Revise: EfficiencyEfficiency = 75 ÷ 100 × 100% = 75%. Arrow shaft widths are proportional to energy.
The fraction of the input energy transferred usefully, often expressed as a percentage.
Specification 3.11, 3.12, 8.15, 13.8 · Paper 1, Paper 2
The fraction of the total energy supplied to a device that is transferred usefully.
Revise: Efficiency EquationEfficiency therefore has no unit.
The proportion of the total energy supplied to a device that is transferred usefully.
The proportion of the supplied energy that is transferred usefully rather than dissipated to the surroundings.
Specification P7.2d, P7.2e, P8.2e · Paper 2 (Foundation), Paper 4 (Higher)
A measure of the fraction of the total input energy that is transferred usefully.
Revise: Calculating efficiencyTheir units cancel, so efficiency has no unit.
The fraction of the input energy transfer that is transferred usefully.
The proportion of input energy transferred usefully, often expressed as a percentage.
Paper 1, Paper 2
Revise: Efficiency and Sankey DiagramsBecause one energy is divided by another, efficiency has no unit. It can be written as a decimal between 0 and 1.
The fraction of the input energy or power that is transferred usefully, often expressed as a percentage.
Efficiency has no unit. Give a decimal between 0 and 1, or multiply it by 100 to give a percentage between 0% and 100%.
For Higher Tier questions about improving efficiency, name the unwanted transfer, state how it is reduced and connect this to a larger useful fraction of the input.
For an explanation of Grid efficiency, give the full chain: step-up transformer increases potential difference → for the same power, current decreases → heating in the cables decreases → less energy is wasted.
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