A loudspeaker produces a sound wave that travels through air. Describe what happens to the air particles as the sound wave passes through them, and explain how this creates regions of compression and rarefaction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Sound waves are an example of a type of wave that transfers energy through a medium by causing particles to vibrate.
Model answer (5 marks)
Air particles vibrate back and forth in the same direction as the wave travels, so the wave is longitudinal.
When the speaker pushes on the air, the particles are forced closer together, creating a region of compression – a higher pressure area.
As the particles move away from each other, a region of rarefaction – lower pressure – is produced.
The particles oscillate about their equilibrium positions; they do not move permanently, so the energy is carried forward by the successive compressions and rarefactions.
When the speaker pushes on the air, the particles are forced closer together, creating a region of compression – a higher pressure area.
As the particles move away from each other, a region of rarefaction – lower pressure – is produced.
The particles oscillate about their equilibrium positions; they do not move permanently, so the energy is carried forward by the successive compressions and rarefactions.
Examiner tips
- Use the term ‘longitudinal wave’ early to gain a point. Show the sequence: compression → rarefaction → compression. Mention that particles return to their original positions to explain energy transfer.
- common_mistakes
- :
- Calling the wave transverse instead of longitudinal. Forgetting to state that particles oscillate rather than move permanently.
Mark scheme (5 marks)
- Air particles vibrate back and forth (oscillate) in the same direction as the wave is travelling
- This makes sound a longitudinal wave
- A compression is where particles are pushed closer together / regions of higher pressure
- A rarefaction is where particles are spread further apart / regions of lower pressure
- Energy is transferred in the direction of wave travel without the particles themselves moving permanently from their position / particles return to their original positions
Key terms in this question
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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