# Explain how ultrasound waves are used in foetal scanning to produce an image of a foetus inside a womb.

> WJEC A-Level Physics (Wales) — 5.3 Electric and magnetic fields (A-Level only) · Explain · 5 marks

> Ultrasound waves have a frequency higher than the upper limit of human hearing, which is 20 kHz. They are used in medicine to produce images of structures inside the body without using harmful radiation.

## Mark scheme (5 marks)

1. Ultrasound waves are emitted/sent into the body (by a probe/transducer)
2. The ultrasound waves are reflected at boundaries between different tissues/structures (e.g. the foetus and surrounding fluid)
3. The reflected waves are detected (by the same probe)
4. The time taken for the waves to return is used to calculate the distance to the reflecting boundary / the position of the foetus
5. This information is processed to build up an image of the foetus

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-ultrasound-waves-are-used-29d5746c) · Published by Druglandscape Ltd.