Science glossary film: Refraction

The change in direction of a wave caused by its change in velocity, as it moves from one medium into another. When a wave passes into a slower medium at an angle, you can imagine one end of the wavefront being slowed down first, which bends the wave into a new direction. We notice the effect most easily with light, but it happens with all waves. 

When a wave passes into a slower medium at an angle, you can imagine one end of the wavefront being slowed down first, which bends the wave into a new direction. We notice the effect most easily with light, but it happens with all waves.