- 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!