# Explain why alternating current (AC) must be used in the primary coil of a transformer, rather than direct current (DC), in order for the transformer to work.

> Edexcel GCSE Physics (1PH0) — 13.1 Electromagnetic induction (Phys only) · Explain · 4 marks

> Transformers are used throughout the National Grid to change the magnitude of voltage. They rely on a changing magnetic field to induce a current in the secondary coil.

## Mark scheme (4 marks)

1. AC in the primary coil produces a continuously changing magnetic field
2. This changing magnetic field cuts through / links with the secondary coil
3. This induces a potential difference / current in the secondary coil
4. DC produces a constant magnetic field, so no change occurs and no potential difference / current is induced in the secondary coil

## Key terms

- [alternating current](https://www.gradenine.co.uk/glossary/alternating-current)
- [direct current](https://www.gradenine.co.uk/glossary/direct-current)
- [primary coil](https://www.gradenine.co.uk/glossary/primary-coil)
- [transformer](https://www.gradenine.co.uk/glossary/transformer)

## Related

- [Revision notes for Edexcel GCSE Physics (1PH0)](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/explain-why-alternating-current-ac-must-a2286cdc) · Published by Druglandscape Ltd.