A student is investigating sound waves travelling through air. Explain what is meant by the terms amplitude, frequency, and wavelength, and describe how the speed of a wave is related to its frequency and wavelength.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Sound waves are longitudinal waves that transfer energy through a medium without transferring matter.
Model answer (5 marks)
Amplitude is the maximum displacement of a particle from its rest/equilibrium position.
Frequency is the number of complete waves (cycles) passing a point per second.
Wavelength is the distance between two successive points that are in phase – the length of one complete wave cycle.
The speed of a wave is given by v = fλ.
For a fixed wave speed, frequency and wavelength are inversely proportional: if the frequency increases the wavelength decreases, and vice versa.
Frequency is the number of complete waves (cycles) passing a point per second.
Wavelength is the distance between two successive points that are in phase – the length of one complete wave cycle.
The speed of a wave is given by v = fλ.
For a fixed wave speed, frequency and wavelength are inversely proportional: if the frequency increases the wavelength decreases, and vice versa.
Examiner tips
- Use the exact definitions – amplitude, frequency, wavelength. Show the equation v = fλ and explain the inverse relationship. Keep the answer concise and to the point.
Common mistakes
- Confusing amplitude with intensity or loudness. Using the wrong equation for wave speed (e.g. v = λ/f). Failing to mention the inverse relationship between frequency and wavelength.
Mark scheme (5 marks)
- Amplitude is the maximum displacement of a particle from its rest/equilibrium position
- Frequency is the number of complete waves (cycles) passing a point per second
- Wavelength is the distance between two successive points that are in phase / the length of one complete wave cycle
- Wave speed equals frequency multiplied by wavelength (v = fλ)
- For a fixed wave speed, frequency and wavelength are inversely proportional / if frequency increases, wavelength decreases (and vice versa)
Key terms in this question
amplitude · frequency · wavelength
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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