How does a ray bend as it passes from one transparent medium to another?
The ‘bending of a ray of light’ when it passes from one substance into another substance is called refraction.
Let us understand by an example:
Consider a ray light travelling from air to glass or water.
Glass and water are thicker and heavier than air. They are said to be ‘denser’ than air.
What happens is that light slows down when it passes from the less dense air into the denser glass or water.
This slowing down of the ray of light also causes the ray of light to change direction. It is the change in the speed of the light that causes refraction.