This key facts covers Key Facts — 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 7 of 13 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
📋 Key Facts — Efficiency
- Efficiency (decimal) = Useful output energy ÷ Total input energy
- Efficiency (%) = (Useful output ÷ Total input) × 100
- Wasted energy = Total input − Useful output
- Energy is always conserved (input = useful output + wasted)
- Efficiency is always less than 100% — thermodynamics forbids 100%
- Most wasted energy becomes thermal energy (heat) in surroundings
- Efficiency can be calculated using power values as well as energy values
- Reducing friction, resistance and drag all improve efficiency
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 decimal
0.85 (between 0 and 1)
As a percentage
85% (multiply decimal by 100)