A student sets up a ripple tank to study water waves. The student observes that the waves have a frequency of 4 Hz and a wavelength of 0.05 m. Explain what is meant by the terms frequency and wavelength, and describe how the wave speed could be determined from these two quantities.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Water waves travel across the surface of a ripple tank. The waves transfer energy from one place to another without transferring matter.
Model answer (5 marks)
Frequency is the number of complete waves passing a fixed point each second.
Wavelength is the distance between two successive points that are in the same phase, for example crest to crest or trough to trough.
The speed of a wave is given by the product of its frequency and its wavelength:
\[v = f\,\lambda\]
Substituting the given values gives
\[v = 4\,\text{Hz} \times 0.05\,\text{m} = 0.20\,\text{m s}^{-1}\].
The waves therefore transfer energy across the surface of the tank without moving the water particles over long distances.
Wavelength is the distance between two successive points that are in the same phase, for example crest to crest or trough to trough.
The speed of a wave is given by the product of its frequency and its wavelength:
\[v = f\,\lambda\]
Substituting the given values gives
\[v = 4\,\text{Hz} \times 0.05\,\text{m} = 0.20\,\text{m s}^{-1}\].
The waves therefore transfer energy across the surface of the tank without moving the water particles over long distances.
Examiner tips
- Define frequency and wavelength in your own words. Show the wave‑speed equation and plug in the numbers. Include the units and the final numerical value. Mention that energy, not matter, is transported.
Common mistakes
- Using the wrong unit for frequency (e.g. s⁻¹ instead of Hz). Confusing wavelength with wavelength of light or other waves. Forgetting to multiply frequency by wavelength or giving the wrong numerical result.
Mark scheme (5 marks)
- Frequency is the number of complete waves (oscillations/cycles) passing a point per second
- Wavelength is the distance from one point on a wave to the equivalent point on the next wave (e.g. crest to crest or trough to trough)
- Wave speed is calculated by multiplying frequency by wavelength (wave speed = frequency × wavelength)
- Correct substitution or statement that wave speed = 4 × 0.05 = 0.2 m/s (or consistent numerical answer showing understanding of the equation)
- Waves transfer energy from one place to another without transferring matter
Key terms in this question
frequency · wavelength · wave speed
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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