A student watches ripples spreading out across the surface of a pond after a stone is dropped into the water. The student notices that a small floating leaf does not move across the pond, even though the ripples pass through it. Describe what is meant by a wave, and use this to explain why the leaf does not travel across the pond.

Eduqas A-Level Physics — 2.4 The nature of waves · Describe · 5 marks · View as Markdown

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

Model answer (5 marks)

A wave is a transfer of energy through a medium without a permanent displacement of the medium.
1. The energy carried by the wave moves through the water.
2. The water particles (and the leaf resting on them) do not travel with the wave; they are not carried along.
3. Instead, the particles vibrate or oscillate up and down as the wave passes.
4. This vibration is perpendicular to the direction in which the wave propagates.
5. When the wave has passed, the particles – and the leaf – return to their original position, so the leaf ends up in the same place.

Examiner tips

  • Use the definition of a wave as energy transfer, not matter movement.
  • Show that particles oscillate perpendicular to wave direction.
  • Explain why the leaf returns to its original position after the wave passes.
  • Keep the answer concise and use the exact terminology from the mark scheme.

Common mistakes

  • Confusing wave motion with particle transport; saying the leaf is carried along.
  • Lacking the detail that the vibration is perpendicular to the wave direction.
  • Failing to state that the leaf returns to its original position after the wave passes.

Mark scheme (5 marks)

  1. A wave is a transfer of energy (not matter/particles)
  2. The water particles (or leaf) do not travel with the wave / are not carried along permanently
  3. The water particles (and therefore the leaf) vibrate / oscillate up and down
  4. The direction of vibration is perpendicular (at right angles) to the direction the wave travels
  5. After the wave has passed, the leaf returns to its original position / the leaf ends up in the same place

Key terms in this question

wave

Related

More The nature of waves questions

▶ Try answering this question with AI marking (free) →