# Explain why the current through a metallic conductor is directly proportional to the potential difference applied across it, using a microscopic model of charge carriers.

> IB DP Physics Higher Level (2023 syllabus) — B.5 Current and circuits · Explain · 4 marks

## Mark scheme (4 marks)

1. A greater potential difference produces a greater electric field within the conductor
2. A greater electric field exerts a greater force on the conduction electrons, giving them a greater mean drift velocity
3. Current is proportional to mean drift velocity (I = nAvq), so if drift velocity doubles when pd doubles, current doubles
4. At constant temperature the frequency of collisions (and hence resistance) remains constant, preserving the linear/ohmic relationship

## Key terms

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

## Related

- [Revision notes for IB DP Physics Higher Level (2023 syllabus)](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/explain-why-the-current-through-a-770e0a19) · Published by Druglandscape Ltd.