JEE Main & Advanced Physics Ray Optics Sample Paper Topic Test - Refraction of Light Through Plane Surfaces

A point source of light is placed at a distance h below the surface of a large deep lake. What is the percentage of light energy that escapes directly from the water surface if \[\mu \] of water \[=\frac{4}{3}\]?

A) 50%

B) 25%

C) 20%

D) 17%

Correct Answer: D

Solution :

[d] The solid angle subtended by area shown by the shaded portion in

\[2\pi \,(1-\cos \,C)\]

So, % going out \[=\frac{2\pi (1-\cos C)}{4\pi }\times 100\]

\[=\frac{1}{2}\,(1-\cos C)\times 100=17%\]

C = critical angle.