# A student places a straight wire horizontally between the poles of a permanent magnet so that the wire is at right angles to the magnetic field. When a current is switched on, the wire moves. When the student reverses the direction of the current, the wire moves in the opposite direction. Describe what determines the direction of the force on the wire, and explain what would happen to the force if the current in the wire were switched off.

> OCR GCSE Physics A: Gateway Science (J249) — P3.3 Magnetism and the motor effect · Describe · 4 marks

> In an investigation into the motor effect, a straight wire is connected to a power supply and placed between the poles of a permanent magnet so that the wire is perpendicular to the magnetic field lines.

## Mark scheme (4 marks)

1. The direction of the force depends on the direction of the current (in the wire)
2. The direction of the force also depends on the direction of the magnetic field
3. If the current is switched off there is no force on the wire
4. A force on a current-carrying conductor in a magnetic field (motor effect) requires both a current AND a magnetic field to be present

## Key terms

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

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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-places-a-straight-wire-79ee96f6) · Published by Druglandscape Ltd.