# Explain how ultrasound waves are used in sonar to determine the distance to an underwater object.

> Eduqas A-Level Physics — 5.2 Gravitational fields (A-Level only) · Explain · 5 marks

> A ship uses sonar to detect objects beneath the water. Ultrasound pulses are sent downwards from the hull of the ship and the returning signals are detected.

## Mark scheme (5 marks)

1. Ultrasound waves are emitted/transmitted from the ship towards the underwater object
2. The ultrasound waves reflect off the underwater object and return to the ship
3. The time taken between emission and detection of the reflected wave is measured
4. The speed of ultrasound in water is known, so the total distance travelled by the wave can be calculated
5. The distance to the object is half the total distance calculated (because the wave travels to the object and back)

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-ultrasound-waves-are-used-bbf51b28) · Published by Druglandscape Ltd.