# A voltmeter is connected in parallel with a filament lamp in a circuit. As the lamp gets brighter, the voltmeter reading increases. Explain why the resistance of the filament lamp increases as its brightness increases.

> Cambridge International IGCSE Physics (0625) — 4.2 Electrical quantities · Explain · 4 marks

> A filament lamp is connected in a simple circuit. As more current passes through the lamp, it glows more brightly and becomes hotter.

## Mark scheme (4 marks)

1. The filament lamp's resistance increases because its temperature increases
2. Greater current through the filament causes the filament to become hotter / the filament heats up as more current passes through it
3. The filament is a metal, so it has free electrons that carry charge / current flows via free electrons
4. At higher temperatures the ions/atoms in the filament vibrate more, making it harder for free electrons to flow / increasing opposition to current flow

## Key terms

- [resistance](https://www.gradenine.co.uk/glossary/resistance)
- [filament lamp](https://www.gradenine.co.uk/glossary/filament-lamp)

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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