Question

A light ray was incident perpendicular to the boundary that separates water from glass. What is the angle of refraction that the light will make? Explain your answer.

Answer 1

When a ray of light falls normally to the surface of a glass slab (or any other medium for that matter) it makes an angle of 0° with respect to its normal. So, i = 0°, now in this case,
n sini = n^' sinr [n and n' are respective refractive indices]
So,
n'sinr = 0
As n cannot be zero so sin⁡r = 0 or angle of refraction is
r = 0.
Thus, no refraction takes place and the ray of light emerges through the medium (of n') unrefracted.
This is why it passes straight through.