GCSE Physics · AQA 8463 · Topic 4.1.2
Conservation and dissipation of energy
Key points
- Conservation of energy: energy can be transferred, stored or dissipated, but the total in a closed system never changes.
- In every real transfer some energy is dissipated (spread out) into less useful stores, usually thermal energy of the surroundings.
- Unwanted transfers can be cut with lubrication (less friction) and thermal insulation (less heating of the surroundings).
- A material with a lower thermal conductivity transfers energy by conduction more slowly. Thicker walls with low conductivity mean a building cools more slowly.
- Efficiency = useful output energy transfer ÷ total input energy transfer, or useful power output ÷ total power input. Multiply by 100 for a percentage.
- Efficiency can be improved by reducing waste, but no device is 100% efficient (except an electric heater, where all output is meant to be thermal).
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Energy can never be created or destroyed, yet we still talk about energy being "wasted". This sub-topic explains that apparent contradiction and shows how engineers reduce waste and how to calculate efficiency.
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