# A security system uses a solenoid to lock a door. When current flows through the solenoid, it produces a magnetic field that holds an iron bolt in place. A technician suggests that increasing the number of turns in the solenoid coil and inserting an iron core will make the lock stronger. Explain why these two changes each increase the strength of the magnetic field produced by the solenoid.

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

> A solenoid is used in a door-locking mechanism. The solenoid must produce a strong enough magnetic field to hold an iron bolt firmly in place. The technician proposes two modifications: increasing the number of turns in the coil, and inserting an iron core into the centre of the solenoid.

## Mark scheme (5 marks)

1. Increasing the number of turns increases the strength of the magnetic field
2. Each turn contributes to the overall field / the fields from each turn align and add together
3. Inserting an iron core increases the strength of the magnetic field
4. The iron core becomes an induced magnet / it is easier for magnetic field lines to pass through iron than air
5. A stronger magnetic field exerts a greater force on the iron bolt, making the lock more secure

## Key terms

- [solenoid](https://www.gradenine.co.uk/glossary/solenoid)
- [magnetic field](https://www.gradenine.co.uk/glossary/magnetic-field)
- [iron core](https://www.gradenine.co.uk/glossary/iron-core)
- [number of turns](https://www.gradenine.co.uk/glossary/number-of-turns)

## 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/a-security-system-uses-a-solenoid-303c3265) · Published by Druglandscape Ltd.