GCSE Physics: Efficiency and Power

Efficiency and power are where GCSE Physics turns the energy model into numbers that matter: how much of the input actually does something useful, and how fast energy is being transferred. This quiz drills both ideas in the calculation formats the exams use.

The efficiency questions run in both directions. The forward direction computes efficiency from useful output and total input — a motor turning 500 J of electrical energy into 400 J of kinetic energy — expressed as a decimal or percentage. The reverse direction, which students find markedly harder, recovers the input from a known output and efficiency: a kettle delivering 2000 J at 80% efficiency must have been supplied 2500 J. A wasted-energy question completes the triangle, finding the 300 J lost by a device that is 40% efficient on a 500 J input.

The power questions treat power strictly as the rate of energy transfer: a bulb consuming 600 J in 10 seconds, a machine doing 1200 J of work in 2 minutes (where the time must first become 120 seconds), and the reverse calculation of energy from power and time for a 500 W motor running for 30 seconds. Unit discipline — joules, watts, seconds and the minute-to-second conversion — is deliberately part of what is being tested.

The conceptual questions cover the practical side the specification pairs with the calculations: why lubrication, streamlining and thermal insulation reduce unwanted transfers, and which everyday scenarios genuinely dissipate significant thermal energy through friction. In line with the 2025–2027 equations sheet provision, no question demands formula recall — the skills are choosing the relationship, rearranging it and keeping units straight. Full worked explanations accompany every answer.

• Calculate efficiency from useful output and total input as a decimal or percentage
• Work backwards from output and efficiency to find input or wasted energy
• Apply power as the rate of energy transfer, converting time units correctly
• Rearrange the power relationship to find energy from power and time
• Explain how lubrication, streamlining and insulation reduce unwanted energy transfers

Topic scope follows the Energy section of the Department for Education's GCSE combined science and physics subject content: efficiency, power as rate of energy transfer, and ways of reducing unwanted energy transfers. Reflects the 2025–2027 arrangement in which an equations sheet is provided, so questions test application rather than formula recall.