Optics Question 957
Question: 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} $ ?
Options:
A) 50%
B) 25%
C) 20%
D) 17%
Show Answer
Answer:
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.
