Question

What will it be the critical angle if light is incident from glass n=1.5 in to the air n=1​

Answer 1

The formula, which is fairly easy to derive, is:

The sine of the critical angle = refractive index of the “refracting medium” divided by refractive index of the “incident medium”.

In this case the “refractive medium” is air and the “incident medium” is glass.

The refractive index of air is about 1 (almost exactly).

So, in this case, the sine of the critical angle is 1 divided by 1.5 = 0.6667.

You will find the answer, from sine tables, to be approximately 41.81 degrees.

Remember that the refractive index of air is slightly more than 1. Using a better value for refractive index of air, I get the critical angle to be about