# Engineers use ultrasound to check for cracks inside large metal components, such as aircraft engine parts, without cutting them open. Explain how ultrasound waves are used to detect a crack inside a metal component, and why ultrasound is suitable for this purpose rather than audible sound.

> OCR A-Level Physics B: Advancing Physics (H557) — 5.3 Astrophysics and cosmology · Explain · 5 marks

> Quality-control engineers at an aircraft maintenance facility direct ultrasound pulses into solid metal engine parts to check for internal cracks. The component does not need to be damaged or cut open during the process.

## Mark scheme (5 marks)

1. Ultrasound waves have a frequency above 20 kHz / above the upper limit of human hearing
2. When the ultrasound pulse reaches the boundary between the metal and the crack (air gap), it is partially reflected back
3. A receiver / detector next to the emitter detects the reflected pulse earlier than a pulse reflected from the far surface
4. The speed of ultrasound in the metal is constant, so the time between emission and detection is used to calculate the position / depth of the crack
5. Ultrasound (rather than audible sound) is used because its short wavelength allows it to detect small cracks / gives greater resolution / detail

## 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/engineers-use-ultrasound-to-check-for-0b79c487) · Published by Druglandscape Ltd.