# A filament lamp and a diode are components used in electrical circuits. Explain why the current through a filament lamp does not increase proportionally as the potential difference across it is increased, and state one way in which the behaviour of a diode differs from that of a filament lamp.

> OCR A-Level Physics B: Advancing Physics (H557) — 3.4 Materials · Explain · 5 marks

> A student is comparing how different components behave when the potential difference across them is changed. She notices that a filament lamp behaves differently from an ohmic conductor, and that a diode behaves differently again.

## Mark scheme (5 marks)

1. As current increases (through the filament lamp), electrons collide with atoms in the filament / resistor
2. These collisions transfer energy to the atoms, causing the filament's temperature to increase
3. The increased temperature causes the atoms to vibrate more, making it harder for electrons to flow
4. Therefore the resistance of the filament lamp increases (as potential difference / temperature increases), so the current does not increase proportionally
5. A diode only allows current to flow in one (forward) direction / has a very high resistance in the reverse direction (so no current flows in reverse), whereas a filament lamp allows current in both directions

## Key terms

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

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-filament-lamp-and-a-diode-1cc0307c) · Published by Druglandscape Ltd.