# A ship uses a search-and-rescue device that contains a coil of wire connected to a detector. When the device is held near a submerged metal object, the changing magnetic field from the object induces a potential difference in the coil. Explain how electromagnetic induction produces a potential difference in the coil and describe two ways the size of the induced potential difference could be increased.

> OCR GCSE Physics A: Gateway Science (J249) — P3.4 Electromagnetic induction · Explain · 4 marks

> A ship uses a search-and-rescue device that contains a coil of wire connected to a detector. When the device is held near a submerged metal object, a changing magnetic field passes through the coil.

## Mark scheme (4 marks)

1. A changing magnetic field (passing through the coil) induces a potential difference / the magnetic field must be changing to induce a potential difference
2. The induced potential difference is due to the change in the magnetic field cutting through / linking with the coil (lines of magnetic field passing through the coil change)
3. First method to increase induced potential difference: increase the number of turns/coils of wire
4. Second method to increase induced potential difference: increase the strength of the magnetic field / use a stronger magnet or move the source of the field closer / faster

## Key terms

- [electromagnetic induction](https://www.gradenine.co.uk/glossary/electromagnetic-induction)
- [induced potential difference](https://www.gradenine.co.uk/glossary/induced-potential-difference)
- [coil](https://www.gradenine.co.uk/glossary/coil)
- [magnetic field](https://www.gradenine.co.uk/glossary/magnetic-field)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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-ship-uses-a-search-and-rescue-device-df9d1339) · Published by Druglandscape Ltd.