A diver is swimming underwater in the sea. The diver hears a boat engine that is some distance away. Explain how the sound from the boat engine is able to travel through the water and reach the diver's ears.

Eduqas GCSE Physics — 5.1 Waves in air, fluids and solids · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The engine vibrates, producing sound waves. These vibrations disturb the water molecules, causing them to oscillate. The oscillating molecules transfer the disturbance to neighbouring molecules, so the vibration propagates through the water. Because water is a liquid medium, sound can travel through it and reach the diver's ears.

Examiner tips

  • Use the word "vibrate" for the engine and water particles
  • Explain that the disturbance is passed from particle to particle
  • Mention that water is a suitable medium for sound
  • Keep the answer concise and use correct terminology

Common mistakes

  • Saying the sound travels through air instead of water
  • Forgetting to mention the transfer of energy between particles
  • Using vague terms like "moves" instead of "vibrates"

Mark scheme (4 marks)

  1. The boat engine causes vibrations / the engine vibrates
  2. The vibrations cause water molecules/particles to vibrate / the water particles are disturbed
  3. The vibrations are passed from one particle to the next / energy is transferred through the water by particles vibrating and passing on the disturbance
  4. Sound can travel through liquids / water is a medium through which sound waves can travel (it does not need air)

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