Units (Waves)
5 marks · NormalThe diagram below shows a water wave produced in a ripple tank. The motor can be set to vibrate at different frequencies.
Explain the difference between a transverse wave and a longitudinal wave. Give one example of each.
The frequency of the water waves is increased while keeping the wave speed constant. Describe and explain what happens to the wavelength.
On a diagram of a transverse wave, label both the amplitude and the wavelength.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) — · must show Transverse: vibrations perpendicular to energy transfer. Example: light OR water surface waves., Longitudinal: vibrations parallel to energy transfer. Example: sound.
(b) — · must show Wavelength decreases as frequency increases if speed is constant., Explanation linking v = f × λ.
(c) — · must show Wavelength labelled as distance between crests or similar points., Amplitude labelled as maximum displacement from rest.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct description of transverse wave and example.
B2 (a) · 1 mark · Correct description of longitudinal wave and example.
M1 (b) · 1 mark · States that the wavelength decreases as frequency increases for constant speed (or correct v = fλ link).
A1 (b) · 1 mark · Explanation is correct and refers to v = fλ relationship.
B3 (c) · 1 mark · Wave diagram with correct labels for amplitude and wavelength.
Worked solution
a) Transverse waves have vibrations at right angles to the direction of energy transfer. Example: light wave or water wave on the surface. Longitudinal waves have vibrations in the same direction as energy transfer. Example: sound wave.
b) If the frequency increases but speed stays constant, the wavelength must decrease. v = f × λ, so if v is constant and f increases, λ decreases.
c) (Draw a transverse wave with crests and troughs, label the distance between two crests as 'wavelength', and the height from the centre to the crest as 'amplitude').