Wavelength and frequency
2 marks · EasyA student increases the frequency of waves made in a stretch of rope while keeping the speed the same. Explain what happens to the wavelength.
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The wavelength decreases because for a constant speed, increasing frequency makes wavelength smaller (wavelength = speed / frequency).
Also accept: The wavelength gets shorter when frequency increases, if speed does not change.
Common mistakes: Thinking wavelength increases with frequency.; Not connecting the effect to the equation.
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Marking points
M1 · 1 mark · States that if speed is constant, wavelength changes when frequency changes.
A1 · 1 mark · Correctly states or implies that wavelength decreases/inverse relationship (using v = f λ, λ = v / f).
Worked solution
From the wave equation, v = f λ. If speed stays constant, increasing frequency means λ (wavelength) must decrease since λ = v / f.