Refraction
Refraction is the change in direction of propagation of a wave due to a change in its transmission medium.the change in direction of a wave passing from one medium to another caused by its change in speed.
For example, waves in deep water travel faster than in shallow. If an ocean wave approaches a beach obliquely, the part of the wave farther from the beach will move faster than that closer in, and so the wave will swing around until it moves in a direction perpendicular to the shoreline.
The speed of sound waves is greater in warm air than in cold. At night, air is cooled at the surface of a lake, and any sound that travels upward is refracted down by the higher layers of air that still remain warm.
Thus, sounds, such as voices and music, can be heard much farther across water at night than in the daytime.
