# A student wraps a long wire into a coil and connects it to a battery. They notice that the magnetic field produced inside the coil is much stronger than the field produced by a single straight wire carrying the same current. The student then pushes an iron rod into the centre of the coil. Explain why the field inside the coil is stronger than that of a single straight wire, and describe how inserting the iron rod affects the magnetic field.

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

> A student is investigating the magnetic field produced by a coil of wire connected to a battery. They compare this to the field produced by a single straight wire carrying the same current, and then investigate the effect of placing an iron rod inside the coil.

## Mark scheme (5 marks)

1. Coiling the wire causes the individual magnetic fields from each turn to align / combine in the same direction
2. This produces a single, large, uniform magnetic field inside the solenoid rather than many separate weaker fields
3. The shape of the solenoid's magnetic field is similar to that of a bar magnet (with a north and south pole)
4. Inserting the iron rod (iron core) increases the strength of the magnetic field
5. Because it is easier for magnetic field lines to pass through iron than through air

## Key terms

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

## 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-student-wraps-a-long-wire-802e122c) · Published by Druglandscape Ltd.