# A student is investigating how the resistance of a wire changes with its length. The student connects a wire to a circuit with a fixed potential difference and measures the current through the wire. The student then repeats the investigation using wires of increasing length, keeping all other variables the same. Explain why a longer wire has a greater resistance than a shorter wire of the same material and thickness.

> OCR A-Level Physics A (H556) — 3.1 Motion · Explain · 5 marks

> A student notices that when a longer wire is used in a circuit, the current measured by the ammeter is lower than when a shorter wire is used, even though the potential difference across the wire stays the same.

## Mark scheme (5 marks)

1. A longer wire contains more atoms (for electrons to interact with / travel through)
2. Electrons collide with the atoms in the wire
3. In a longer wire there are more collisions (between electrons and atoms)
4. These collisions make it more difficult for electrons to flow / slow the electrons down
5. Therefore resistance is greater (in a longer wire) / current is lower for the same potential difference

## Key terms

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

## 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-student-is-investigating-how-the-267a7fbd) · Published by Druglandscape Ltd.