A wave travels along the surface of water in a ripple tank. Explain what is meant by the terms frequency, wavelength, and wave speed, and state the relationship between these three quantities.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Frequency is the number of complete waves passing a fixed point per second.
Wavelength is the distance between two successive identical points on a wave, such as crest to crest or trough to trough.
Wave speed is the distance travelled by the wave pattern per second.
The relationship is v = fλ.
If the frequency increases while the wave speed remains constant, the wavelength must decrease (and vice‑versa).
Wavelength is the distance between two successive identical points on a wave, such as crest to crest or trough to trough.
Wave speed is the distance travelled by the wave pattern per second.
The relationship is v = fλ.
If the frequency increases while the wave speed remains constant, the wavelength must decrease (and vice‑versa).
Examiner tips
- Use the exact definitions and the formula v = fλ. Show the link by giving a clear example of how a change in one quantity affects the others. Keep the answer concise and avoid unnecessary wording.
Common mistakes
- Confusing frequency with wavelength or speed. Using the wrong formula (e.g. v = λ/f). Failing to explain the effect of changing one quantity on the others.
Mark scheme (5 marks)
- Frequency is the number of complete waves (oscillations/cycles) passing a point per second
- Wavelength is the distance between two successive identical points on a wave (e.g. crest to crest or trough to trough)
- Wave speed is the distance travelled by the wave per second (or the speed at which the wave pattern moves through the medium)
- Wave speed equals frequency multiplied by wavelength (v = fλ)
- Correct use of the relationship to describe how the quantities are linked — e.g. if frequency increases and wave speed stays constant, wavelength decreases (or equivalent valid statement showing understanding of the relationship)
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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