Explain how the amplitude and frequency of a wave are related to the energy it carries, and distinguish between the effect of increasing amplitude and increasing frequency on the energy transported by a mechanical wave travelling through a medium.

IB DP Physics Higher Level (2023 syllabus) — C.2 Wave model · 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 energy carried by a wave is proportional to the square of its amplitude and also to the square of its frequency. Increasing the amplitude increases the maximum displacement of the particles in the medium, so each particle has greater kinetic and potential energy as it oscillates. Increasing the frequency increases the rate at which energy is transferred because particles complete more oscillations per unit time, so the power (energy per unit time) delivered by the wave is greater.

Examiner tips

  • Use the proportionality statements (E∝A² and E∝f²) to cover the first two points.
  • Explain the physical meaning of amplitude and frequency in terms of particle motion and energy.
  • Mention power when discussing frequency to show the rate of energy transfer.

Mark scheme (4 marks)

  1. The energy carried by a wave is proportional to the square of its amplitude.
  2. The energy carried by a wave is also proportional to the square of its frequency.
  3. Increasing the amplitude increases the maximum displacement of the particles in the medium, so each particle has greater kinetic and potential energy as it oscillates.
  4. Increasing the frequency increases the rate at which energy is transferred because particles complete more oscillations per unit time, so the power (energy per unit time) delivered by the wave is greater.

Key terms in this question

amplitude · frequency · energy · mechanical wave

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