This exam tips covers Exam Tips for Efficiency within Efficiency for GCSE Physics. Revise Efficiency in Energy for GCSE Physics with 19 exam-style questions and 4 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 12 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
💡 Exam Tips for Efficiency
🎯 Common Question Types:
- Calculate efficiency as a decimal or percentage (2-3 marks)
- Draw or interpret a Sankey diagram (3-4 marks)
- Explain why efficiency is always less than 100% (2 marks)
- Calculate wasted energy from input and efficiency (2 marks)
- Compare efficiency of two devices from data (2-3 marks)
📝 Key Command Words:
- Calculate: Show formula, substitution, and answer with no unit (efficiency is a ratio)
- Draw: Sankey diagram — use a ruler, make widths proportional
- Explain: Refer to energy dissipation into surroundings as thermal energy
- Compare: State which device is more efficient and give a numerical reason
⚠️ Common Mistakes to Avoid:
- Giving efficiency a unit — it has no unit (it is a ratio)
- Getting input and output confused in the formula — useful output always goes on top
- Saying energy is "lost" — always say "wasted" or "dissipated as thermal energy"
- Drawing Sankey diagrams where arrow widths do not add up correctly
Practice questions for Efficiency
Which equation correctly defines efficiency?
Explain one method that can be used to reduce unwanted energy transfers in a machine and state how it reduces waste.
Quick recall flashcards
As a percentage
85% (multiply decimal by 100)
As a decimal
0.85 (between 0 and 1)