# Ultrasound waves are used in sonar and foetal scanning. Explain how ultrasound waves are used in sonar to determine the distance to an underwater object, and state ONE reason why ultrasound rather than sound within the range of human hearing is used for this purpose.

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

## Mark scheme (5 marks)

1. Ultrasound waves are emitted/transmitted from the device towards the object
2. The ultrasound waves reflect off the object and are detected
3. The time between emission and detection of the reflected wave is measured
4. The distance is calculated using the wave velocity and the measured time (with awareness that the wave travels to the object and back)
5. Ultrasound is used because its frequency is above the upper limit of human hearing (above 20 kHz) so it does not disturb humans / or because it can be directed in a narrow beam / or because it has a shorter wavelength giving better resolution

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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/ultrasound-waves-are-used-in-sonar-15c17b5f) · Published by Druglandscape Ltd.