# An electric motor uses a current-carrying coil of wire placed between the poles of two permanent magnets. Explain how the motor produces continuous rotation.

> OCR A-Level Physics B: Advancing Physics (H557) — 4.4 Waves · Explain · 5 marks

> Electric motors are found in many everyday devices, from electric toothbrushes to electric vehicles. They rely on the interaction between a magnetic field and a current-carrying conductor.

## Mark scheme (5 marks)

1. The current-carrying wire in a magnetic field experiences a force (motor effect / force on a wire)
2. The two sides of the coil that are perpendicular to the magnetic field experience forces in opposite directions
3. These opposing forces cause the coil to rotate
4. Fleming's left-hand rule can be used to determine the direction of the force, with thumb showing force, first finger showing magnetic field direction, and second finger showing current direction
5. A split-ring commutator reverses the current direction every half turn so that the forces always act in the same rotational direction, allowing continuous rotation

## Key terms

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

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/an-electric-motor-uses-a-current-carrying-ab6b5602) · Published by Druglandscape Ltd.