Refraction

2 marks · Easy

Describe what happens to a sound wave as it passes from warm air into cold air, and explain your answer in terms of wave properties.

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The sound wave slows down and changes direction. This is because sound travels faster in warm air than in cold air, so when entering cold air, the change in speed causes refraction and bending of the wave.

Also accept: The sound wave bends because it slows down when entering cold air.

Common mistakes: Sound does not change speed.

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Marking points

M1 · 1 mark · States or implies that the sound wave slows down in cold air.

M1 · 1 mark · Explains that this change in speed causes refraction or a change in direction.

Worked solution

Sound waves travel more slowly in cold air. As the wave passes from warm air into cold air, it slows down and its direction changes (the wave is refracted).