A teacher demonstrates waves on a slinky spring by pushing and pulling one end back and forth along the length of the spring. Explain how energy is transferred along the spring and describe the motion of the coils of the spring during this demonstration.

WJEC A-Level Physics (Wales) — 2.4 The nature of waves · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

The teacher creates a longitudinal wave. The energy moves along the spring while the coils themselves do not travel with the wave; they only oscillate. Each coil vibrates parallel to the length of the spring, alternating between being pushed together (compression) and pulled apart (rarefaction).

Examiner tips

  • Use the term "longitudinal wave" to gain the first point.
  • Explain that the coils do not move along the spring – they only oscillate – to cover the second point.
  • Describe the oscillation direction and link it to compression and rarefaction to hit all remaining points.

Common mistakes

  • Calling the wave transverse instead of longitudinal.
  • Saying the coils travel along the spring rather than oscillating.
  • Omitting the distinction between compression and rarefaction.

Mark scheme (5 marks)

  1. The waves produced are longitudinal waves
  2. Energy is transferred along the spring without matter being transferred / the coils of the spring do not travel along the spring
  3. The coils vibrate / oscillate parallel to the direction of energy transfer / along the length of the spring
  4. Areas of compression (coils closer together) are produced
  5. Areas of rarefaction (coils further apart) are produced

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