Efficiency — GCSE Physics Revision
Revise Efficiency for GCSE Physics. Step-by-step explanation, worked examples, common mistakes and exam-style practice aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP.
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Go to National & Global Energy ResourcesWhat is Efficiency?
Efficiency is a measure of how much useful energy you get out of a device compared to the total energy you put in. It is usually expressed as a percentage. No device is 100% efficient; some energy is always wasted, usually as heat.
Board notes: Covered by all major boards (AQA, Edexcel, OCR) at both Foundation and Higher tiers.
Step-by-step explanationWorked example
A light bulb is supplied with 100J of electrical energy and it produces 20J of light energy. Calculate its efficiency. Solution: Efficiency = (Useful Energy Out / Total Energy In) x 100%. Efficiency = (20J / 100J) x 100% = 20%.
Mini lesson for Efficiency
1. Understand the core idea
Efficiency is a measure of how much useful energy you get out of a device compared to the total energy you put in. It is usually expressed as a percentage.
Can you explain Efficiency without copying the notes?
2. Turn it into marks
A light bulb is supplied with 100J of electrical energy and it produces 20J of light energy. Calculate its efficiency.
Underline the method, evidence, or command-word move that would earn credit in GCSE Energy.
3. Fix the likely mark leak
Watch for this mistake: Stating that efficiency can be greater than 100%. This is impossible as it would violate the principle of conservation of energy.
Write one correction rule before doing another practice question.
Practise this topic
Jump into adaptive, exam-style questions for Efficiency. Free to start; sign in to save progress.
Efficiency practice questions
These are original StudyVector questions for revision practice. They are not official exam-board questions.
Question 1
In one GCSE sentence, explain what Efficiency is testing.
Answer: Efficiency is a measure of how much useful energy you get out of a device compared to the total energy you put in. It is usually expressed as a percentage.
Mark focus: Precise definition and topic focus.
Question 2
A Efficiency question uses an unfamiliar context. What should the answer do before adding detail?
Answer: It should name the process, variable, equation, particle model, or evidence being tested, then explain the result using precise scientific vocabulary.
Mark focus: Method selection and command-word control.
Question 3
A student makes this mistake: "Stating that efficiency can be greater than 100%. This is impossible as it would violate the principle of conservation of energy." What should their next repair task be?
Answer: Do one Efficiency question and review the mistake type.
Mark focus: Error correction and next-step practice.
Efficiency flashcards
Core idea
What is the main idea in Efficiency?
Efficiency is a measure of how much useful energy you get out of a device compared to the total energy you put in. It is usually expressed as a percentage.
Common mistake
What mistake should you avoid in Efficiency?
Stating that efficiency can be greater than 100%. This is impossible as it would violate the principle of conservation of energy.
Practice
What is one useful practice task for Efficiency?
Answer one Efficiency question and review the mistake type.
Exam board
How should you use board notes for Efficiency?
Covered by all major boards (AQA, Edexcel, OCR) at both Foundation and Higher tiers.
Common mistakes
- 1Stating that efficiency can be greater than 100%. This is impossible as it would violate the principle of conservation of energy.
- 2Confusing useful energy with wasted energy. Efficiency is about the useful output, not the total input or the wasted part.
- 3Leaving efficiency as a decimal instead of a percentage. The question will usually specify the required format.
Efficiency exam questions
Exam-style questions for Efficiency with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel, OCR, WJEC, Eduqas, CCEA, Cambridge International (CIE), SQA, IB, AP specifications.
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Step-by-step method
Step-by-step explanation
4 steps · Worked method for Efficiency
Core concept
Efficiency is a measure of how much useful energy you get out of a device compared to the total energy you put in. It is usually expressed as a percentage. No device is 100% efficient; some energy is …
Frequently asked questions
How can you improve the efficiency of a device?
Efficiency can be improved by reducing the amount of wasted energy. For example, by lubricating moving parts to reduce friction, or by using insulation to reduce heat loss.
Why can't a machine be 100% efficient?
In any real-world machine, some energy is always converted into non-useful forms, such as heat due to friction or air resistance. This wasted energy means that the useful output energy is always less than the input energy.