A student sets up a stretched string fixed at both ends and plucks it to produce a stationary wave. Explain how the stationary wave is formed and describe the difference between a node and an antinode.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Two waves of the same frequency and wavelength travel in opposite directions along the string. The waves superpose, producing a stationary wave. A node is a point of zero displacement – the string does not vibrate there. An antinode is a point of maximum displacement – the string vibrates with maximum amplitude. Nodes and antinodes are fixed in position; energy is not transmitted along the string.
Examiner tips
- Use the term ‘superposition’ or ‘interference’ to show understanding of wave overlap.
- Mention that the string is fixed at both ends, giving nodes at the ends.
- Show the difference between node (zero amplitude) and antinode (maximum amplitude).
Common mistakes
- Confusing nodes with antinodes or vice versa.
- Failing to state that the waves travel in opposite directions before superposition.
- Not recognising that the energy does not travel with the stationary wave.
Mark scheme (5 marks)
- Two waves (of the same frequency/wavelength) travel in opposite directions along the string
- The two waves overlap (superpose/interfere) to produce the stationary wave
- A node is a point of zero displacement / the string does not vibrate at a node
- An antinode is a point of maximum displacement / the string vibrates with maximum amplitude at an antinode
- Nodes and antinodes are fixed in position / energy is not transmitted along the string (the wave does not travel)
Key terms in this question
stationary wave · node · antinode
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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