7. Types of waves and their properties (12 minutes) - Pearson

Answers:
LEVEL: AS
PHYSICS – Waves and Oscillations
7. Types of waves and their properties (12 minutes)
(a)
(i) Explain what is meant by the term 'progressive wave'.
(1 mark)
A progressive wave spreads out energy from the source vibration into the surrounding space.
(ii) A radio wave of wavelength 5 x 103 m travels through a vacuum at 3 x 108 ms -1 . Calculate the
frequency of this wave.
(3 marks)
v = fλ
∴ f = v/λ
= 3 x 10 8 ms -1 ÷ 5 x 10 3 m
= 6 x 10 4 s -1
= 6 x 10 4 Hz
Watch out!
If a question mentions an electromagnetic wave (e.g. radio, microwave, etc.) travelling in a vacuum, you should
immediately realize that it will be travelling at 3 x 10 8 ms -1 .
(b)
(i) Explain what is meant by the term 'standing wave'.
(2 marks)
Under certain circumstances the energy of a wave can be prevented from spreading out. The positions of the
peaks and troughs of these ‘standing’ or ‘stationary’ waves do not move.
(ii) A standing wave is established in a string. Each antinode is separated from its neighbour by 12.5 cm.
What is the wavelength of the standing wave
(2 marks)
Antinodes are separated by λ/2 so λ = 25 cm
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Answers:
LEVEL: AS
PHYSICS – Waves and Oscillations
(c)
(i) Explain why the wave produced in this experiment is longitudinal.
(1 mark)
It is longitudinal because the vibrations causing the wave moving in the same direction as the wave motion.
(ii) On the diagram label:
a compression (C)
a rarefaction (R)
the wavelength (λ) of the wave
(3 marks)
By presenting information in a slightly unusual way (e.g. many teachers demonstrate slinky wires on a
horizontal surface rather than hanging vertically as shown here) some questions can ‘weed out’ the weaker
students.
(Total marks 12)
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