Wavelength and frequency
2 marks · EasyA science teacher says, “If you halve the frequency of a wave and keep its speed the same, you double the wavelength.” Explain why this is correct.
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Must show: wavelength is inversely proportional to frequency, explanation using v = f λ
Also accept: If v stays the same and f is halved, λ must double because v = fλ.
Common mistakes: says wavelength does not change; does not mention the wave equation
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Marking points
M1 · 1 mark · Explains that wavelength is inversely related to frequency.
B1 · 1 mark · Uses the wave equation to justify this relationship.
Worked solution
Since wave speed v is constant and v = fλ, when frequency (f) is halved, wavelength (λ) must double for the product to stay the same. This means if you halve the frequency, wavelength becomes twice as long.