# An electric motor is used to drive a conveyor belt in a food packaging factory. Explain how the electric motor produces continuous rotation.

> OCR A-Level Physics B: Advancing Physics (H557) — 4.2 Energy, power and resistance · Explain · 5 marks

> An electric motor contains a coil of wire that is free to rotate between two permanent magnets. When a direct current is passed through the coil, the motor begins to spin and keeps spinning as long as the current flows.

## Mark scheme (5 marks)

1. A current-carrying coil of wire in a magnetic field experiences a force
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 on each side of the coil
5. The motor continues to rotate because a split-ring commutator reverses the current direction every half turn, maintaining the direction of rotation

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/an-electric-motor-is-used-to-5b883201) · Published by Druglandscape Ltd.