A police siren produces a sound wave. Explain what is meant by the amplitude and frequency of this sound wave, and describe how each property affects what a listener hears.

Eduqas GCSE Physics — 1.5 Features of waves · Explain · 4 marks · View as Markdown

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

A police car drives past a bystander, sounding its siren. The siren produces a sound wave that travels through the air to the bystander's ears.

Model answer (4 marks)

Amplitude is the maximum displacement of a particle from its rest position. A greater amplitude makes the sound louder, so amplitude determines the loudness or volume of the sound.
Frequency is the number of complete waves (cycles) that pass a point each second. A higher frequency gives the sound a higher pitch, so frequency determines the pitch of the sound.

Examiner tips

  • Use the exact definitions of amplitude and frequency.
  • Explain how amplitude affects loudness and how frequency affects pitch.
  • Show the relationship between amplitude and volume, and frequency and pitch.
  • Keep the answer concise and to the point.

Common mistakes

  • Confusing amplitude with wavelength or frequency with wavelength.
  • Saying amplitude affects pitch or frequency affects loudness.
  • Using vague terms like ‘size’ or ‘strength’ instead of ‘maximum displacement’ and ‘cycles per second’.

Mark scheme (4 marks)

  1. Amplitude is the maximum displacement of a particle from its rest/equilibrium position
  2. Greater amplitude means the sound is louder / amplitude determines the loudness (volume) of the sound
  3. Frequency is the number of complete waves (cycles/oscillations) passing a point per second
  4. Higher frequency means the sound has a higher pitch / frequency determines the pitch of the sound

Key terms in this question

amplitude · frequency

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