Sound Waves
4 marks · NormalA sound wave travels from a warm region into a cooler region of air.
Name the process that happens to the sound wave as it passes into the cooler region.
Explain, with reference to the speed of sound, why the direction of the wave changes.
Describe one real-life example where this process makes sounds easier to hear over long distances.
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.
Show answer
(a) Refraction
(b) The speed of sound decreases in the cooler region. As a result, the direction of the wave bends (changes), which is called refraction.
(c) Sounds carry further across a lake early in the morning (or other accepted contextual scenarios) due to refraction.
Common mistakes: Not mentioning change in speed; Confusing reflection and refraction
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Names process as refraction.
M1 (b) · 1 mark · Mentions change in speed in cooler region.
B1 (b) · 1 mark · Links change of direction to refraction due to speed change.
B1 (c) · 1 mark · Gives context where sound is heard more clearly due to refraction (e.g. across a lake in the morning).
Worked solution
a) Refraction.
b) The sound travels more slowly in cooler air than in warm air. When the wave passes into the cooler region its speed changes, causing the wave to change direction (refract).
c) Across a lake early in the morning, sounds can be heard more easily due to refraction of sound waves by cool air near the water surface.