Question

White light is incident on the interface of glass–air, as shown in the Fig. If green light is just totally internally reflected, then the emerging rays, in air would have in them, the colours

(1) yellow, orange, red

(2) violet, indigo, blue

(3) all seven colours of white light

(4) all the other six colours of white light (exept green)

Answer 1

(1) yellow, orange, red

Let μ be the refractive index of glass for light of wave length λ. We know μ α 1/λ². Also,

where k is a constant 

The angle of incidence, for green colour, equals the critical angle. For light of λ more than that of the green colour, the critical angle would be more than that for green. Only these colours would not undergo T.I.R and would emerge out. Therefore, yellow, orange and red (having λ > λ_g) would emerge out.