Lesson 3 of 9

Conservation of energy

Goal: Explain that energy is conserved but spreads out.

Puzzles for this lesson

Energy cannot be created or destroyed. The total is the same before and after every change.

This is the law of conservation of energy. Energy is only ever transferred from one store to another.
Some energy is always dissipated. It spreads out into the thermal store of the surroundings, where it is much less useful. We call this wasted energy.
A filament lamp wastes most of its energy. Of every 100 J supplied to it, only about 5 J is transferred as light. The rest heats the lamp and the room.

wasted energy = total energy supplied − useful energy

Your turn

This lesson’s activity starts here in a moment.

I can state that the total energy stays the same.I can work out how much energy is wasted.

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Thermal store Filled when an object is warmed up

Conservation of energy Energy cannot be created or destroyed

Dissipated Spread out wastefully into the surroundings

For teachers: AQA 3.3.2 · Pearson Edexcel 28.3, 29.1 · Cambridge 7Pf.02, 9Pf.03