# Sonar and foetal scanning both use ultrasound waves. Explain why ultrasound waves are used in these applications rather than sound waves that humans can hear, and describe what happens to the ultrasound waves in each application to produce useful information.

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

> Ultrasound waves are used in a range of technologies, including sonar systems on ships and medical foetal scanning.

## Mark scheme (5 marks)

1. Ultrasound waves have a frequency higher than the upper limit of human hearing (20 kHz) / are beyond human hearing range
2. Ultrasound is used because it does not damage/harm tissue or the foetus / is safe to use on the body (compared to some other wave types)
3. In sonar, ultrasound waves are emitted into water and reflected back from objects / the sea bed
4. In sonar, the time taken for the reflected wave to return is used to determine the distance to the object
5. In foetal scanning, ultrasound waves are emitted into the body and reflected at boundaries between different tissues / the foetus and surrounding fluid, and the reflected waves are detected and processed to form an image

## Key terms

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

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/sonar-and-foetal-scanning-both-use-9f8af1b9) · Published by Druglandscape Ltd.