Energy Efficiency
Efficiency is the fraction of input energy that becomes useful output energy, usually given as a percentage.
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Efficiency is the fraction of input energy that becomes useful output energy, usually given as a percentage.
- Efficiency equals useful output over total input
- No machine is 100 percent efficient
- Wasted energy spreads to the surroundings
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Energy Efficiency?
Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Energy Efficiency. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.
Check that you can explain Energy Efficiency in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Energy Efficiency explains how the physical world behaves, from sport and transport to electricity and medicine.
Energy Efficiency in detail
Efficiency measures how much of the energy supplied to a device is transferred usefully: efficiency = useful output energy ÷ total input energy (× 100 for a percentage). No device is 100% efficient, because some energy is always dissipated as heat or sound.
An LED bulb might be about 80–90% efficient, compared with 5% for a filament bulb. Improving efficiency by insulation, lubrication or better design saves money and reduces fossil fuel use. Efficiency is always less than 1 (or 100%), and any answer above this indicates a mistake.
How the interactive helps you understand Energy Efficiency
Watch the bar chart in the interactive. Use any sliders or buttons it offers to change the values and see how the bar chart responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Energy Efficiency.
Real-life uses and examples
- Use Energy Efficiency to make sense of a practical and its results.
- Answer “explain” questions by linking Energy Efficiency to a clear cause and effect.
- Predict what a ball, car or circuit will do with Energy Efficiency before you do the calculation.
Common mistakes to avoid
- Mixing up Energy Efficiency with a related quantity that has different units.
- Forgetting that some quantities, such as force or velocity, also have a direction.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Energy Efficiency
What is Energy Efficiency?
Efficiency is the fraction of input energy that becomes useful output energy, usually given as a percentage.
What are the most important points about Energy Efficiency?
The main points are: Efficiency equals useful output over total input; No machine is 100 percent efficient; Wasted energy spreads to the surroundings.
Why is Energy Efficiency useful?
Understanding Energy Efficiency explains how the physical world behaves, from sport and transport to electricity and medicine.
How can I practise Energy Efficiency?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Energy Efficiency?
Related topics in Physics include Simple Machines, Impulse and Collisions, Kinetic Theory of Matter.