# A technician is testing two resistors made from different materials. Resistor A is made from carbon and has a higher resistance than Resistor B, which is made from a metal alloy. Explain why Resistor A has a higher resistance than Resistor B, and describe what would happen to the resistance of Resistor B if its temperature were increased.

> WJEC A-Level Physics (Wales) — 2.1 Conduction and resistance · Explain · 5 marks

> Resistor A is made from carbon. Resistor B is made from a metal alloy. Resistor A has a higher resistance than Resistor B at room temperature.

## Mark scheme (5 marks)

1. Metals (alloys) contain free electrons that can move through the material
2. Carbon has fewer free electrons (charge carriers) available, so current flows less easily
3. Fewer charge carriers means greater resistance to the flow of current in carbon
4. Increasing the temperature of Resistor B causes the metal ions/atoms to vibrate more
5. More vibration means free electrons collide more frequently with ions, so resistance increases

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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-technician-is-testing-two-resistors-561ffd7e) · Published by Druglandscape Ltd.