Efficiency compares useful output with total input. It has no unit and can be written as a decimal or percentage.
Multiply the fraction by 100 to express it as a percentage.
Move the slider to compare devices with different useful output fractions. This comparison does not show a change over time.
A motor receives 200 J and transfers 150 J usefully.
Useful output cannot exceed total input: efficiency cannot be greater than 1 or 100%.
For calculations, use useful output = efficiency as a decimal × total input.
Compare devices doing the same useful job. A higher power does not necessarily mean a higher efficiency.
A 90%-efficient device transfers a greater fraction usefully than a 60%-efficient one, but total input energy also depends on how much work is needed and how long it runs.
Higher Tier only
Reduce unwanted transfers so a greater fraction of the input does the intended job. For example, lubricate a motor’s bearings to reduce friction, or insulate a hot-water tank to reduce transfer to the surroundings.
Always link the change to less unwanted transfer → a greater useful fraction.
Efficiency = useful output / total input. Multiply by 100 for a percentage. Higher Tier: explain how reducing unwanted transfers improves efficiency.
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