Refraction of Light: Isosceles Prism of 120°, Refractive Index 1.44

[harsh95]

An isosceles prism of angle 120* has a refractive index 1.44.Two parallel monochromatic rays enter the prism parallel to each other as shown in figure.the ray emerge from the opposite faces-
(A)Are parallel to each other
(B)are diverging
(C) make an angle 2[sin^ -1(0.72)-30*] with each other
(D) make an angle 2 sin^ -1(0.72) with each other
The figure for the following question is attached .

The possible eqn. are Refractive index=Sin i/Sin r

It is one of the MCQ in my question paper, But I am unable to solve it.Since the rays fall normal to the surface of the prism, so they should go undeviated but what after they strikes the next prism surface ,How will they deviate?

Only thing i am able to do is that they will enter the prism without any deviation since it is perpendicular to the surface of the prism but what after that?

The answer (C) but how?
Thank you,
Harsh

 

[rl.bhat]

Let ABC be the prism with AC a the base.Let the parallel rays meet the other faces at P and Q. draw a perpendicular RBD to AC. Draw normals at P and Q.
Now you can see that the angle of incidence in the glass is 30 degrees. Find the angle of refraction in the air. Simple geometry will show you that angle of refraction i equal to 30 + angle PRD. And 2*angle PR is the reacquired answer.