# A filament light bulb transfers electrical energy into light. Explain why the filament light bulb is not 100% efficient and describe what happens to the energy that is not usefully transferred.

> WJEC GCSE Physics (Wales) — 1.6 Distance, speed and acceleration · Explain · 4 marks

> A filament light bulb is connected to the mains electricity supply. Its purpose is to provide light for a room.

## Mark scheme (4 marks)

1. The useful energy transfer is electrical energy to light (energy)
2. Some energy is transferred as heat/thermal energy, which is a waste energy transfer
3. Because of conservation of energy, energy cannot be created or destroyed, so the total output energy equals the input energy but not all of it is useful
4. The waste thermal energy is dissipated/transferred to the surroundings, warming the air around the bulb

## Related

- [Revision notes for WJEC GCSE Physics (Wales)](https://www.gradenine.co.uk/learn)
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