# A filament lamp is connected in series with a diode and a battery. Explain what happens to the resistance of the filament lamp as the current through it increases, and describe what effect the diode has on the current in the circuit when the battery is connected in reverse.

> OCR A-Level Physics A (H556) — 3.4 Materials · Explain · 5 marks

> Filament lamps contain a thin metal filament that heats up when current flows through it. Diodes are components that only allow current to flow in one direction.

## Mark scheme (5 marks)

1. As current increases, the filament's temperature increases
2. The electrons collide with the vibrating atoms in the filament, transferring energy to them
3. The increased vibrations of the atoms make it harder for electrons to flow, so resistance increases
4. When the battery is reversed, the diode has a very high resistance in that direction
5. Therefore no current (or negligible current) flows in the circuit when the battery is reversed

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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-in-1797d583) · Published by Druglandscape Ltd.