Question

PQR is a right angled prism with other angles as 60⁰ and 30⁰. Refractive index of prism is 1.5. PQ has a thin layer of liquid. Light falls normally on the face PR. For total internal reflection, maximum refractive index of liquid is

• A. 1.4
• B. 1.3
• C. 1.2
• D. 1.6

Answer 1

Answer: (C)

1.2

Answer 2

For TIR at PQ $\theta < C$

From geometry of figure $\theta = 60$ i.e.

$60 > C \Rightarrow \sin 60 > \sin C$

$\Rightarrow \mu _ { \text {Liquid } } < \frac { \sqrt { 3 } } { 2 } \times 1.5 \Rightarrow \mu _ { \text {Liquid } } < 1.3$