# A security door system uses an electromagnet to hold a heavy metal door shut. When the electromagnet is switched on, it holds the door closed. When a correct code is entered, the electromagnet is switched off and the door can be opened. Explain how the electromagnet works and why the door is attracted to it when the current is switched on.

> OCR A-Level Physics A (H556) — 4.1 Charge and current · Explain · 5 marks

> An electromagnet consists of a solenoid wound around an iron core. The door contains an iron plate on its inner face.

## Mark scheme (5 marks)

1. A solenoid is a coil of wire / wire wound into a coil
2. When current flows through the solenoid / wire, a magnetic field is produced around it
3. The iron core increases the strength of the magnetic field / makes it a stronger electromagnet
4. The iron plate in the door becomes an induced magnet when placed in the magnetic field
5. Induced magnetism always causes attraction / the induced pole facing the electromagnet is always opposite, so the door is attracted

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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-security-door-system-uses-an-391c1370) · Published by Druglandscape Ltd.