# Sonar is used by ships to detect objects beneath the surface of the water. Describe how sonar works and explain why ultrasound waves, rather than sound waves within the human hearing range, are used for this purpose.

> Eduqas A-Level Physics — 5.3 Electric and magnetic fields (A-Level only) · Describe · 5 marks

> A ship uses sonar equipment to map the seabed and detect shoals of fish beneath it.

## Mark scheme (5 marks)

1. Ultrasound waves are emitted from the ship (into the water)
2. The ultrasound waves reflect off the object / seabed / fish and return to the ship
3. The time taken for the waves to return is measured / used to calculate distance
4. Ultrasound waves have a frequency higher than the upper limit of human hearing (above 20 kHz)
5. Ultrasound has a shorter wavelength so can detect smaller objects / gives a more detailed / precise image

## Key terms

- [sonar](https://www.gradenine.co.uk/glossary/sonar)
- [ultrasound waves](https://www.gradenine.co.uk/glossary/ultrasound-waves)

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Source: [GradeNine](https://www.gradenine.co.uk/q/sonar-is-used-by-ships-to-511c2fa8) · Published by Druglandscape Ltd.