Aray of light bends upon entering a new medium. what is this phenomenon called?

Refraction

Explanation:

Refraction is a phenomenon which results when a ray of light enters from one medium to another medium. The speed of light in a medium slows down. It depends upon the optical density of the medium which is given by refractive index.

When a ray of light enters from rarer medium to denser medium, it bends towards the normal.

When a ray of light enters from denser medium to rarer medium, it bends away from the normal.

The laws of refraction are:

This is Snell's law. i is the angle of incidence, r is the angle of refraction, n₁ is the refractive index of medium 1 and n₂ is the refractive index of the medium 2.