Question

A ray of light is incident normally on a plane glass slab. What will be
(i) the angle of refraction and
(ii) the angle of deviation for the ray?

Answer 1

Hint: As we all know that the only condition, the angle of incidence is equal to the angle of refraction when the ray is un-deviated or the angle of deviation is zero.Practically the angle of deviation is never zero, it must be some small values.

Complete answer:
The ray of light which is incident normally on a plane glass slab passes undeviated.That is, such a ray suffers no bending at the surface because here the angle of incidence is ${0^\circ }$. So, if the ray of light is un-deviated, that means the angle of deviation is zero.And we all know that- when the angle of deviation is zero, then the angle of incidence is equal to the angle of refraction. So, as we see above, the angle of incidence is ${0^\circ }$ , then the angle of refraction is also ${0^\circ }$.

This is essentially impossible since light must refract when it enters a medium from another medium. As a result, the angle of minimal deviation is never zero, but it might be extremely small. If the light suffers minimum deviation, the angle of incidence is never equal to the angle of refraction. The angle of incidence, on the other hand, is equal to the angle of emergence.
(i) The angle of refraction is ${0^\circ }$ and,
(ii) The angle of deviation of the ray is also ${0^\circ }$.

Note: If the incident and refracted rays make identical angles with the prism faces, the angle of deviation is the smallest. When it comes to prism spectroscopes, the angle is quite important because it can be easily determined.