# A filament lamp is connected to a battery in a simple circuit. The battery has an electromotive force (EMF) of 6 V. When the circuit is switched on, the lamp glows and the connecting wires become slightly warm. Explain why the lamp and the wires become warm, and describe how this affects the efficiency of the circuit.

> Edexcel A-Level Physics (9PH0) — 3.2 EMF, resistance and circuits · Explain · 5 marks

> A student notices that after a filament lamp has been switched on for several minutes, both the lamp and the connecting wires feel warm to the touch. The battery supplying the circuit has an electromotive force (EMF) of 6 V.

## Mark scheme (5 marks)

1. The battery (EMF) transfers energy to the charges / electrons in the circuit
2. The resistance of the lamp (and wires) causes energy to be transferred as heat / thermal energy
3. The heat produced by the wires is waste energy / not the intended useful output of the circuit
4. Efficiency is the ratio of useful output energy to total input energy
5. Because energy is wasted as heat (in wires and as heat from the lamp), the efficiency of the circuit is less than 1 / less than 100%

## Key terms

- [electromotive force (EMF)](https://www.gradenine.co.uk/glossary/electromotive-force-emf)
- [efficiency](https://www.gradenine.co.uk/glossary/efficiency)

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-filament-lamp-is-connected-to-d6438374) · Published by Druglandscape Ltd.