# A ship uses sound waves to detect the depth of the ocean floor beneath it. A pulse of sound is sent straight downwards from the ship. The echo is detected 3.0 seconds later. Explain how the properties of sound waves make this depth-finding technique possible, and describe how the crew would use the time measurement to determine the depth of the ocean floor.

> Pearson Edexcel International GCSE Physics (4PH1) — 3.3 Light and sound · Explain · 4 marks

> Sound travels at approximately 1500 m/s in sea water. The technique of using reflected sound pulses to find the depth of water is known as echo sounding.

## Mark scheme (4 marks)

1. Sound waves are longitudinal waves that can travel through a medium (sea water) / sound requires a medium to travel through
2. The sound pulse is reflected at the ocean floor / the echo is the reflected sound wave returning to the ship
3. The total distance travelled by the sound is twice the depth (the sound travels to the floor and back)
4. The depth is calculated using speed = distance / time (or depth = speed × half the recorded time), giving depth = 1500 × 1.5 = 2250 m

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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-sound-waves-to-9737d1a9) · Published by Druglandscape Ltd.