# A ship uses sonar to detect the seabed. An ultrasound pulse is sent downwards from the ship and an echo is detected 0.6 seconds later. The speed of sound in seawater is 1500 m/s. Explain how sonar works and describe what happens to the ultrasound pulse between being emitted and being detected.

> Edexcel A-Level Physics (9PH0) — 4.1 Stress, strain and the Young modulus · Explain · 5 marks

> Sonar is used by ships to determine the depth of water beneath them. A pulse of ultrasound is emitted downwards from the hull of the ship.

## Mark scheme (5 marks)

1. Ultrasound is a sound wave with a frequency higher than the upper limit of human hearing (above 20 000 Hz / 20 kHz)
2. The ultrasound pulse travels downward through the water towards the seabed
3. The pulse reflects (bounces back) at the boundary between the water and the seabed
4. The reflected pulse (echo) is detected back at the ship
5. The time taken for the pulse to travel to the seabed and back can be used to calculate the depth of the water

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-ship-uses-sonar-to-detect-c41a4875) · Published by Druglandscape Ltd.