A student makes waves on the surface of water in a tank. The waves travel at a speed of 0.6 m/s and have a frequency of 3 Hz. Explain what is meant by the terms frequency and wavelength, and describe how the student could use the wave speed equation to find the wavelength of these water waves.

Eduqas A-Level Physics — 2.5 Wave properties · Explain · 5 marks · View as Markdown

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

Waves transfer energy from one place to another without transferring matter. All waves have properties including amplitude, frequency, wavelength and wave speed.

Model answer (5 marks)

Frequency is the number of complete waves passing a point per second.
Wavelength is the distance from one crest to the next crest (or trough to trough).
The wave speed equation is v = f\,\lambda.
Rearranging gives λ = v ÷ f.
Substituting v = 0.6 m s⁻¹ and f = 3 Hz gives λ = 0.6 ÷ 3 = 0.2 m.

Examiner tips

  • Use the exact definitions of frequency and wavelength. Show the wave speed equation and correctly rearrange it. Insert the numerical values and keep units.
  • Remember to state the units of wavelength (m).

Common mistakes

  • Confusing frequency with wavelength. Using the wrong formula (e.g. v = λ × f but solving for v instead of λ).

Mark scheme (5 marks)

  1. Frequency is the number of complete waves (oscillations/cycles) passing a point per second
  2. Wavelength is the distance from one point on a wave to the equivalent point on the next wave (e.g. crest to crest / trough to trough)
  3. State the wave speed equation: wave speed = frequency × wavelength
  4. Rearrange the equation correctly to find wavelength: wavelength = wave speed ÷ frequency
  5. Correctly substitutes values to give wavelength = 0.6 ÷ 3 = 0.2 m

Key terms in this question

frequency · wavelength · wave speed

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