6.2.3.2 Refraction of Sound Waves

Experiment 1

Result

Explanation

1. Carbon dioxide is denser than air.
2. The sound wave is refracted approaching the normal when the wave propagates from the air into the balloon, and away from normal when moving out from the balloon.
3. As a result, the balloon acts as a biconvex lens and converge the sound wave at a point.

Experiment 2

Result

The amplitude of the sound wave decreases when a balloon filled with Carbon dioxide is placed between the speaker and the microphone.

Explanation

1. Helium gas is less dense than air.
2. The sound wave is refracted away from the normal when the wave propagates from the air into the balloon, and closer to the normal when moving out from the balloon.
3. As a result, the wave is diverged to a wider area and causes the amplitude of the sound wave decreases.



Phenomenon Related to Refraction of Sound Wave





Observation

The sound of a distance train is clearer at night.



Explanation

At night, the air closer to the ground is cooler than the air further from the ground.
Sound wave travels slower in cool air. As a result, the sound wave is refracted in the path of curve towards the ground instead of spreading to a wider area (as at daytime).