Question

To trace the path of a light ray through a glass slab, the angle of incidence is given as 60 degree, two students P&Q found the angle of refraction to be 45 degree & 65 degree. Who is correct?

Answer 1

We know that the speed of light is the fastest in air. So, air is the most optically rarer medium and hence we can say that the glass slab is a optically denser medium as compared to air. So, when a light ray enters from a optically rarer medium to optically denser medium, we know that, light ray bends towards the normal. We can also say that in such a case ( when light is entering from optically rarer to optically denser medium) the angle of incidence will be greater than the angle of refraction. So, the one who has answered 45 degree as the angle of refraction has the correct reading. The other student was wrong because he answered 65 degrees and, as we have discussed above, the angle of refraction cannot be greater than the angle of incidence.