# A bat navigates in complete darkness by emitting pulses of ultrasound and detecting the echoes that return from objects in its surroundings. Explain how the bat is able to locate an insect using this method, and explain why the bat cannot use visible light for this purpose in the same way.

> OCR A-Level Physics B: Advancing Physics (H557) — 5.2 Circular motion and gravitational fields · Explain · 5 marks

> Bats are nocturnal mammals that hunt insects at night. They emit ultrasound pulses from their mouths or noses and their large ears detect the returning echoes. Bats can detect insect prey in total darkness with remarkable precision.

## Mark scheme (5 marks)

1. The ultrasound pulses travel outward and are partially reflected back at the boundary between the insect and the surrounding air (medium).
2. The bat's ears detect the reflected (echo) pulses that return.
3. The speed of the ultrasound waves is constant, so the time between emitting the pulse and receiving the echo tells the bat the distance to the insect.
4. Ultrasound has a frequency above 20 kHz, which is above the upper limit of human hearing, but bats can detect it; this also means the pulses are not audible to insects, giving the bat a hunting advantage.
5. Visible light cannot be used in the same way in total darkness because there is no external source of visible light to reflect off the insect; ultrasound is actively emitted by the bat itself so it does not rely on any external source.

## Key terms

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

## 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)
- [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-bat-navigates-in-complete-darkness-d054a260) · Published by Druglandscape Ltd.