# A student says that ultrasound waves are used in both sonar and foetal scanning because, in both cases, the time taken for an ultrasound pulse to return is measured. Explain how ultrasound is used in sonar to determine the distance to an object underwater, and describe ONE way in which foetal scanning is similar to sonar and ONE way in which its purpose is different.

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

> Ultrasound waves have a frequency higher than the upper limit of human hearing (20 kHz). They can be emitted from a device, travel through a medium, reflect off a boundary, and be detected on return.

## Mark scheme (5 marks)

1. Ultrasound pulses are emitted from a device and travel through the water
2. The ultrasound reflects off the object (boundary) and returns to a detector
3. The time taken for the pulse to return is measured and used to calculate the distance to the object
4. Similarity: foetal scanning also uses the emission, reflection, and detection of ultrasound pulses (same process as sonar)
5. Difference in purpose: sonar is used to determine distances to objects underwater, whereas foetal scanning is used to produce an image of a foetus in a womb

## 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/a-student-says-that-ultrasound-waves-6e315561) · Published by Druglandscape Ltd.