# A cinema uses two types of lighting in its foyer: a set of filament lamps and a set of LED spotlights. Both sets of lights produce the same brightness. The filament lamps each operate at a potential difference of 230 V with a current of 0.5 A. The LED spotlights each operate at the same potential difference but draw only 0.04 A. Explain why the cinema should replace all its filament lamps with LED spotlights, using the concepts of power and energy transfer.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.3 Work, energy and power · Explain · 5 marks

> A cinema manager is reviewing the electricity costs of the foyer lighting. Both the filament lamps and the LED spotlights produce the same useful light output, but the manager notices the electricity bills differ significantly depending on which type of lighting is used.

## Mark scheme (5 marks)

1. Power is the rate at which an appliance transfers energy (or: power = current × potential difference / P = IV)
2. The filament lamp has a greater power than the LED spotlight (e.g. filament lamp power is 115 W; LED power is 9.2 W)
3. Because both types produce the same brightness (same useful light output), the filament lamp wastes more energy / transfers more energy to the surroundings as heat
4. Energy transferred equals power multiplied by time (E = Pt or E = IVt), so over the same time period the filament lamp transfers more energy from the supply
5. Therefore the LED spotlights transfer less energy from the supply for the same light output, reducing electricity costs / making them the more economical/efficient choice

## Key terms

- [power](https://www.gradenine.co.uk/glossary/power)
- [potential difference](https://www.gradenine.co.uk/glossary/potential-difference)
- [current](https://www.gradenine.co.uk/glossary/current)
- [energy](https://www.gradenine.co.uk/glossary/energy)
- [rate](https://www.gradenine.co.uk/glossary/rate)

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-cinema-uses-two-types-of-7bd8a717) · Published by Druglandscape Ltd.