GCSE Physics resources
AQA GCSE Energy
Efficiency compares the useful output with the total input; it does not measure how quickly a device works.
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Efficiency compares the useful output with the total input. An efficiency improvement must name the unwanted transfer and the design change that reduces its rate, such as lubrication reducing friction or insulation reducing heating.
Core learning content
Start with this short teaching sequence for Efficiency and Unwanted Energy Transfers. Read the model, use the visual, then test your recall before moving into examples and exam practice.
Efficiency compares the useful output with the total input. An efficiency improvement must name the unwanted transfer and the design change that reduces its rate, such as lubrication reducing friction or insulation reducing heating.
Useful energy transfer is not the same as all energy transfer. A motor can give a useful kinetic output while heating its surroundings through friction. Improving efficiency means reducing a named unwanted pathway, not claiming that the input energy has disappeared.
Choose a relationship because of the physical change in the question, not because it is familiar. Kinetic energy: Eₖ = ½mv² (J, kg, m/s). Gravitational potential energy: Eₚ = mgh (J, kg, N/kg, m). Elastic potential energy: Eₑ = ½ke² (J, N/m, m). Keep the unit next to each value while you substitute.
State the equation, identify useful and total values, give a percentage if requested, then explain the unwanted pathway in words. Before writing, underline the command word and identify the information that matters. Keep a calculation as equation, substitution and answer with unit; keep an explanation as a linked chain using because, so or therefore. Finish by checking that the final sentence answers the exact context in the question and that the number, direction or conclusion agrees with the evidence given.
Retrieval practice
Answer without looking back first. The feedback explains the model, so a wrong answer still helps you learn.
Mini quiz 1
Mini quiz 2
Mini quiz 3
Try it
How does useful output affect the energy dissipated by a device?
What to notice: the readout and written explanation remain available if you do not use the controls.
Worked examples
Cover the answer, attempt the method and then compare your physics language as well as the number.
Efficiency = 0.70 = 70%.
Insulation reduces energy transfer by heating through the roof, so the house’s thermal energy is transferred to the surroundings more slowly.
Efficiency = 0.75, or 75%.
Misconception clinic
Each of these is tempting because it sounds almost right. Replace it with the precise physics before you meet it in a question.
Independent practice
Use the working space first. Reveal the guidance only after you have committed to an answer, then improve the exact part that would gain the next mark.
24 ÷ 40 = 0.60, so 60%.
It is transferred through unwanted pathways, usually to thermal stores of the machine and surroundings.
It reduces friction, reducing unwanted transfer to thermal stores.
20 ÷ 80 = 0.25, or 25%.
Some energy is transferred to thermal stores by electrical resistance or friction.
It has been transferred to less useful stores, not destroyed.
Questions pupils ask
Energy questions become easier when you name the system, track the stores that change and identify the transfer pathway. Then choose an equation only when the physical change requires it.
Read the snapshot, attempt the worked examples without looking, complete the mini quizzes and then use the practice questions to check your wording and method.
Next step
Physics sticks when you move between explanation, retrieval and application.