Beams of Red, Green and Blue light are incident normally on a right angled prism. The refractive indices are given as µ_R = 1.39, µ_G = 1.44 and µ_B = 1.47. Then the colour which emerges out of face AC will be:

only Red

The correct answer is Option (1) → only Red

for total internal refraction, (i) angle of incidence > critical angle ($i_c$)

and,

$\frac{\sin i}{\sin r}=\frac{μ_1}{μ_2}$ [Snell's law]

$\frac{\sin i}{\sin r}=\frac{1}{μ}$

$∵\sin 45°>\frac{1}{μ}$  [For total internal reflection]

$μ>\sqrt{2}=1.414$

and,

$μ_{red}=1.37<1.414$ → only this will emerge out

$μ_{green}=1.44<1.414$

$μ_{blue}=1.47<1.414$