# Explain how the amplitude of a standing wave varies along its length, and distinguish between a node and an antinode in terms of the energy of the standing wave.

> IB DP Physics Standard Level (2023 syllabus) — C.4 Standing waves and resonance · Explain · 4 marks

> A standing wave is established on a string stretched between two fixed supports.

## Mark scheme (4 marks)

1. The amplitude of a standing wave is not uniform along its length but varies from zero at nodes to a maximum at antinodes.
2. A node is a point of zero displacement / zero amplitude where destructive superposition of the two travelling waves is permanent.
3. An antinode is a point of maximum displacement / maximum amplitude where constructive superposition of the two travelling waves is permanent.
4. Nodes carry no energy / have zero kinetic and potential energy, whereas antinodes carry maximum energy, so energy is not uniformly distributed along a standing wave (unlike a progressive wave).

## Key terms

- [standing wave](https://www.gradenine.co.uk/glossary/standing-wave)
- [node](https://www.gradenine.co.uk/glossary/node)
- [antinode](https://www.gradenine.co.uk/glossary/antinode)
- [amplitude](https://www.gradenine.co.uk/glossary/amplitude)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](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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