# A maglev train uses powerful electromagnets beneath the train carriage and along the track. When current flows through the electromagnets, the train is levitated above the track and pushed forward. Explain how changing the current supplied to the electromagnets beneath the train affects the force experienced by the train, and state two ways, other than changing the current, that the strength of an electromagnet could be increased.

> OCR A-Level Physics B: Advancing Physics (H557) — 4.1 Charge and current · Explain · 5 marks

> Maglev (magnetic levitation) trains have no wheels and do not touch the track. They use electromagnets — solenoids with iron cores — to both levitate and propel the carriage. Engineers can adjust the electrical supply to control the levitation force.

## Mark scheme (5 marks)

1. Increasing the current increases the strength of the magnetic field produced by the electromagnet
2. A stronger magnetic field produces a greater force on the train (force is proportional to the magnetic flux density / field strength)
3. Decreasing the current decreases the magnetic field strength and therefore decreases the force (correct direction of change stated)
4. First correct method to increase electromagnet strength (other than current): increase the number of turns/coils of wire
5. Second correct method to increase electromagnet strength (other than current): use an iron core / change the core material to iron (if not already stated) OR increase the length of the coil OR increase the cross-sectional area of the coil

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-maglev-train-uses-powerful-electromagnets-8679bc2b) · Published by Druglandscape Ltd.