AQA GCSE Physics
AQA GCSE Physics 4.1.2.2 Efficiency Exam Questions
Free AQA GCSE Physics exam questions for 4.1.2.2 Efficiency, with a mark scheme for every pack. Covers efficiency equations using energy and power, expressing efficiency as a decimal or percentage, and ways to increase efficiency.
4.1.2.2 Efficiency exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Physics 4.1.2.2 Efficiency
Efficiency in AQA GCSE Physics measures how much of the energy supplied to a device is transferred usefully. You need two equations, one using energy and one using power, and you must express efficiency as a decimal or a percentage. This section sits in the Energy topic on Paper 1, but efficiency calculations also appear with motors, transformers and electrical appliances. Higher tier students must also describe ways to increase the efficiency of an intended energy transfer. Examiners commonly test rearranging the equation to find useful output or total input, and explaining why no device is 100% efficient.
What you need to know
- Efficiency using energy Efficiency = useful output energy transfer / total input energy transfer.
- Efficiency using power Efficiency = useful power output / total power input. Both equations must be memorised.
- Decimal or percentage Efficiency may be given as a decimal between 0 and 1, or multiplied by 100 to give a percentage. Efficiency has no units.
- Wasted energy Wasted energy = total input energy minus useful output energy. It is usually dissipated to the thermal store of the surroundings.
- Increasing efficiency (Higher tier only) Describe ways to increase the efficiency of an intended energy transfer, such as lubricating moving parts to reduce friction, using thermal insulation, streamlining to reduce air resistance and using wires with low resistance.
- Why never 100% In any real device some energy is always dissipated, so efficiency is always less than 1 (100%). An answer above 100% means the useful and total values have been swapped.
Common mistakes in 4.1.2.2 Efficiency
- Putting useful and total the wrong way round, giving an efficiency greater than 1. Useful output always goes on top.
- Adding units such as J or W to an efficiency. Efficiency is a ratio with no units.
- Writing 0.75% when the decimal is 0.75. Either give 0.75 or 75%.
- Forgetting to convert a percentage to a decimal before rearranging, for example using 40 instead of 0.40.
Try three 4.1.2.2 Efficiency exam-style questions
1. A motor has a total power input of 500 W and a useful power output of 350 W. Calculate its efficiency as a percentage. (2 marks)
Show the mark scheme answer
Efficiency = 350 / 500 = 0.70; = 70%.
2. A light bulb is 15% efficient. It is supplied with 2400 J of energy. Calculate the energy wasted. (3 marks)
Show the mark scheme answer
Useful energy = 0.15 x 2400 = 360 J; wasted energy = 2400 minus 360; = 2040 J.
3. Higher tier: Suggest two ways the efficiency of an electric motor could be increased. (2 marks)
Show the mark scheme answer
Lubricate the bearings or moving parts to reduce friction; use wires with lower resistance (or thicker wires) to reduce heating in the coils; (accept reduce air resistance or improve cooling design where justified).
4.1.2.2 Efficiency FAQs
What does AQA GCSE Physics 4.1.2.2 Efficiency cover?
It covers calculating efficiency from energy or power values, giving it as a decimal or percentage, and (Higher tier) describing ways to increase efficiency.
Which efficiency equations do I need?
Learn efficiency = useful output energy / total input energy and efficiency = useful power output / total power input. Both are recall equations, not on the equation sheet.
How do I check an efficiency answer?
It must be between 0 and 1 as a decimal (or 0 to 100%). If it is bigger, you have swapped the useful and total values.
