A light ray is incident normally on the face AB of a right-angled prism `ABC (mu==1.50)` as shown in figure. What is the largest angle `phi` for which the light ray is totally reflected at the surface AC ?

Options

A. yellow, orange and red colours
B. violet, indigo and blue colours
C. all colours
D. all colours except green

Answer

A

Explanation

Wavelength `(lambda)` increases in the sequence of VIBGYOR. According to Cauchy.s formula, `(mu)` decreases as wavelength increases. Therefore, `mu` decreases in the sequence VIBGYOR.
As, `C=sin^(-1)((1)/(mu))`, therefore, critical anglr C increases in the sequence VIBGYOR. For green colour, `/_i=C`. For yellow, orange and red, critical angle is greater. Therefore, `/_is less thasn critical angle for YOR. These colours will not suffer total internal reflection. They will emerge from glass-air interface.