# Explain why a current-carrying conductor experiences a force when placed in a magnetic field, and describe how the direction of this force can be reversed.

> OCR GCSE Physics A: Gateway Science (J249) — P3.3 Magnetism and the motor effect · Explain · 4 marks

> An engineer is testing a simple electric motor. She notices that when current flows through a wire inside a magnetic field, the wire moves. She wants to understand why this happens and how to control the direction of movement.

## Mark scheme (4 marks)

1. The current-carrying conductor produces its own magnetic field
2. This magnetic field interacts with the external magnetic field
3. The interaction of the two fields produces a force on the conductor (the motor effect)
4. The direction of the force can be reversed by reversing either the current direction or the direction of the magnetic field (not both)

## Key terms

- [magnetic field](https://www.gradenine.co.uk/glossary/magnetic-field)
- [current-carrying conductor](https://www.gradenine.co.uk/glossary/current-carrying-conductor)
- [force](https://www.gradenine.co.uk/glossary/force)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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/explain-why-a-current-carrying-conductor-experiences-53bda58a) · Published by Druglandscape Ltd.