A student places their ear against a long metal railway track and hears a distant train's vibrations through the metal before hearing the same sound through the air. Explain why the student hears the sound through the metal first, and state what type of wave sound is.

Cambridge International IGCSE Physics (0625) — 3.4 Sound · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Sound travels through solids, liquids, and gases, but its speed differs between these media.

Model answer (4 marks)

Sound travels faster in a solid than in a gas because the metal is more rigid and its particles are closer together, so the vibration energy is transferred more quickly.
The train’s sound reaches the student through the track and through the air over the same distance, so the wave that arrives first must be the one that travelled faster.
Thus the student hears the vibration through the metal first.
Sound is a longitudinal wave.

Examiner tips

  • Use the key phrase ‘sound travels faster in a solid’ to gain a point. Explain the role of particle spacing and rigidity. State that the distance is the same for both media. Finish by naming the wave type – longitudinal.”]
  • common_mistakes
  • :
  • Saying ‘sound travels faster in metal’ without explaining why. Confusing the wave type – writing ‘transverse’ instead of ‘longitudinal’. Forgetting to mention the equal distance travelled by both waves.

Mark scheme (4 marks)

  1. Sound travels faster in metal/solids than in air/gases
  2. Because the metal is a more rigid/denser medium, particles are closer together so energy is transferred more quickly
  3. Sound travels the same distance through both media (the length of the track), so the one that arrives first must have travelled faster
  4. Sound is a longitudinal wave

Key terms in this question

vibration

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