Question

Why the light ray bends towards normal from rarer medium to dender medium during refraction

Answer 1

You see refraction is governed by 2 laws. One of it is the snell's law. It says that

sin i/sin r=n2/n1

where n2 and n1 are refractive indexes of medium 2 and 1 respectively.

Consider medium 1 as a rarer medium and 2 as a denser medium.

Now - n2/n1 =v1/v2

So sin i/sin r =v1/v2

v1>v2

v1/v2>1

From above eq.

sin i/sin r >1

sin i>sin r

Sine of angle is equal to angle itself for small angles.

i>r

So the ray moves towards the normal since angle of refraction is less than angle of incidence.