Physics Form 5: Chapter 1 - Refraction of Sound Wave

• During day, the layers of air near the ground is warmer than the layers of air higher up.
• Air layer near the ground is less dense.
• Therefore, sound wave is bent toward the normal.

•  At night, the layers of air near the ground is cool faster than the layers of air higher up.
•  Air layer near the ground is denser.
• Sound travels faster in warm air than in cool air resulting increasing of wavelength.
• When the angle of incidence is larger than the critical angle, total internal reflection occurs.
• Therefore, the path of the sound curves reflects downwards and you can hear the sound easily at night.

Click on the diagram below to play!