# A relay is an electrical switch that uses an electromagnet to control a second, separate circuit. Explain how a relay uses electromagnetism to switch on a high-current device such as a motor.

> Eduqas GCSE Physics — 2.5 Magnetism and electromagnetism · Explain · 4 marks

> Relays are widely used in cars to allow a low-current switch on the dashboard to safely control high-current devices such as starter motors.

## Mark scheme (4 marks)

1. When current flows through the coil of wire, it creates a magnetic field around the coil / the coil becomes an electromagnet
2. The magnetic field magnetises the iron core, making it a stronger magnet / the iron core is attracted and pulls the armature
3. The attracted armature closes the contacts / completes the second (high-current) circuit
4. When the current in the coil is switched off, the magnetic field disappears and the armature returns / the second circuit is broken again (because an electromagnet is only magnetic when current flows)

## Key terms

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

## Related

- [Revision notes for Eduqas GCSE Physics](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-relay-is-an-electrical-switch-5cc35f7b) · Published by Druglandscape Ltd.