Why does refraction occur || Refraction of light | lambda 

refraction, in physics, the change in direction of a wave passing from one medium to another caused by its change in speed. For example, waves travel faster in deep water than in shallow. If an ocean wave approaches a beach obliquely, the part of the wave farther from the beach will move faster than the part closer in, and so the wave will swing around until it moves in a direction perpendicular to the shoreline.