- 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
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.
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)