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.
Topic position
Section 12 of 13
Practice
19 questions
Recall
4 flashcards
💡 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