What is refraction ? What is the cause of refraction ?
When a light ray enters from one medium to another medium, then it deviates from its path. This phenomenon is called refraction of light. Cause of Refraction: The speed of light in denser medium (glass) is less than rarer medium (air). Hence it is clear that when light enters in the denser medium from rarer medium its speed becomes slow, on the other hand when it enters from denser to the rarer medium, it's speed increases. Hence phenomenon of refraction takes place due to difference in speed of travelling from one medium to another.