Edexcel GCSE Combined Science Physics 1SC0
Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves
Light and the Electromagnetic Spectrum
Radioactivity
Energy – Forces Doing Work
Forces and Their Effects
Electricity and Circuits
Magnetism and the Motor Effect
Electromagnetic Induction
Particle Model
Conservation of Energy
Efficiency and how to increase it
- 3 things to know
- Paper 5
Overview
The efficiency equation, why efficiency has no unit, calculating efficiency, useful energy, energy supplied and energy wasted, and increasing efficiency by lubrication, streamlining, LED lamps and insulated pipes, though never to 100%.
What you need to know
Answer each one before you reveal it.
State the equation used to calculate the efficiency of a device.
A device is supplied with 120 J and usefully transfers 30 J. Calculate its efficiency.
Questions from this subtopic
Each one with the model answer underneath.
- 1
State the equation used to calculate the efficiency of a device.
Model answer
Efficiency = useful energy transferred by the device ÷ total energy supplied to the device.
- 2
Explain why efficiency has no unit.
Model answer
It is the ratio of two energies, so the units cancel.
- 3
A device is supplied with 120 J and usefully transfers 30 J. Calculate its efficiency.
Model answer
Efficiency = 30 ÷ 120 = 0.25.
- 4
A lamp is supplied with 200 J and transfers 15 J as light. Calculate its efficiency as a percentage.
Model answer
Efficiency = (15 ÷ 200) × 100 = 7.5%.
- 5
A device with an efficiency of 0.8 is supplied with 500 J. Calculate the useful energy it transfers.
Model answer
Useful energy = 0.8 × 500 = 400 J.
- 6
A machine usefully transfers 90 J and has an efficiency of 0.6. Calculate the total energy supplied to it.
Model answer
Total energy = 90 ÷ 0.6 = 150 J.
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