# A medical team uses ultrasound waves to produce an image of a foetus inside a womb. Explain how ultrasound waves are used to produce this image, and why ultrasound is chosen for this purpose rather than X-rays.

> OCR A-Level Physics B: Advancing Physics (H557) — 5.1 Thermal physics · Explain · 5 marks

> Foetal scanning is a routine medical procedure used to monitor the development of an unborn baby. The scanning device is placed on the surface of the mother's body and both emits and detects ultrasound waves.

## Mark scheme (5 marks)

1. Ultrasound waves are partially reflected at boundaries between different media (e.g. between tissues/organs or the foetus and surrounding fluid)
2. The remainder of the waves continue (are transmitted) through into the next medium
3. The speed of ultrasound waves is constant, so the time between emission and detection of the reflected waves is used to determine the distance to the reflecting boundary
4. Reflections from multiple boundaries allow an image of the foetus to be built up / a receiver next to the emitter detects the reflected waves to form the image
5. Ultrasound is used instead of X-rays because X-rays can cause cell damage / mutations / are harmful to the developing foetus, whereas ultrasound is non-invasive and safe

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](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/a-medical-team-uses-ultrasound-waves-eadbbfa1) · Published by Druglandscape Ltd.