A sound wave travelling through air enters a solid wall. State and explain what happens to the frequency, wavelength, and speed of the sound wave as it passes from air into the solid.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The frequency remains unchanged.
The speed increases as the wave enters the denser solid.
The wavelength increases.
Because speed = frequency × wavelength, and frequency is constant, the wavelength must increase when the speed increases.
The speed increases as the wave enters the denser solid.
The wavelength increases.
Because speed = frequency × wavelength, and frequency is constant, the wavelength must increase when the speed increases.
Examiner tips
- State that frequency is unchanged first. Explain that speed rises in the solid. Show the relationship v= fλ to justify the wavelength change.
- common_mistakes
- :
- Saying the frequency changes. Claiming the wavelength decreases. Forgetting to link speed and wavelength with the equation.
Mark scheme (4 marks)
- The frequency remains unchanged / stays the same
- The speed increases as the wave enters the more dense solid medium
- The wavelength increases
- Correct reasoning linking speed and wavelength: because speed = frequency × wavelength, and frequency is constant, wavelength must increase when speed increases
Key terms in this question
frequency · wavelength · speed
Related
- All Cambridge International IGCSE Physics (0625) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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