This definitions covers Key Definitions 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 6 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
📖 Key Definitions
- Efficiency
- The ratio of useful output energy to total input energy. Can be expressed as a decimal (0 to 1) or percentage (0% to 100%). Always less than 1 (or 100%) in real devices.
- Useful energy output
- The energy transferred in the desired, intended form (e.g., kinetic energy from a motor, light from a bulb).
- Wasted energy
- Energy transferred in an unintended, unwanted form — most commonly as thermal energy (heat) due to friction or resistance. Wasted energy = total input − useful output.
- Sankey diagram
- A flow diagram where arrow widths are proportional to the energy they represent. Used to visualise energy transfers and identify wasted energy.
- Dissipated energy
- Energy that has been spread out into the thermal energy store of the surroundings, making it difficult to recover and use again.
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)