# Explain why sounds above 20 000 Hz are not heard by most adults, and why older adults often lose the ability to hear high-frequency sounds before they lose the ability to hear low-frequency sounds.

> AQA A-Level Physics (7408) — 3.10.2 Physics of the Ear · Explain · 5 marks

> The human ear can detect sounds across a range of frequencies. This range changes with age.

## Mark scheme (5 marks)

1. The audible range for humans is approximately 20 Hz to 20 000 Hz
2. Sounds above 20 000 Hz do not cause the hair cells / receptor cells in the cochlea to respond / send electrical signals to the brain
3. Different parts of the cochlea / basilar membrane respond to different frequencies
4. Hair cells that respond to high frequencies are found near the base / entrance of the cochlea and are exposed to more mechanical stress / vibration
5. Once hair cells are damaged / destroyed they are not replaced, so hearing at those frequencies is permanently lost

## Key terms

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

## Related

- [Revision notes for AQA A-Level Physics (7408)](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/explain-why-sounds-above-20-000-a614de4f) · Published by Druglandscape Ltd.