Question

If the critical angle for the medium of prism is $C$ and the angle of prism is $A$, then there will be no emergent ray when-

• A. $A<2C$
• B. $A=2C$
• C. $A>2C$
• D. $A\ge 2C$

Answer 1

The correct option is C $A>2C$

Let $r_1$ be the angle of refraction at first face

and $r_2$ be the angle of refraction at second face.

as $r_1+r_2=A$

thus, $r_1+r_2>2C.$

This is possible if $r_2>C$

( as if $r_1>C$ incident ray would not enter the prism).

$r_2>C$ implies no emergent ray.

Hence, Option $C$ is correct.