# A student builds a solenoid by wrapping insulated wire into a coil. When a current flows through the solenoid, a magnetic field is produced. Explain how the strength of the magnetic field produced by the solenoid could be increased, and explain why inserting an iron core into the centre of the solenoid also increases the field strength.

> OCR A-Level Physics B: Advancing Physics (H557) — 4.5 Quantum physics · Explain · 5 marks

> A student notices that the solenoid they have built can only pick up a small number of steel paper clips. They want to make the solenoid more powerful without changing the battery or the wire material.

## Mark scheme (5 marks)

1. Increasing the number of turns (coils) of wire increases the field strength
2. Increasing the current through the solenoid increases the field strength
3. Any other valid factor: increasing the length of the coil OR increasing the cross-sectional area
4. Iron is a magnetic material, so inserting an iron core means the field lines pass through the core more easily than through air
5. The iron core becomes an induced magnet, adding to the overall magnetic field of the solenoid

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

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-builds-a-solenoid-by-b65c6b70) · Published by Druglandscape Ltd.