Optics Question 991
Question: A point source of light is placed 4 m below the surface of water of refractive index 5 / 3. The minimum diameter of a disc which should be placed over the source on the surface of water to cut?off all light coming out of water is
[CBSE PMT 1994; JIPMER 2001, 02]
Options:
A) 2 m
B) 6 m
C) 4 m
D) 3 m
Show Answer
Answer:
Correct Answer: B
Solution:
Here $ \sin i=\frac{1}{\mu }=\frac{3}{5} $ .
and hence $ \tan i=\frac{3}{4}=\frac{r}{4} $ .
This gives $ r=3m $ , hence diameter = $ 6m $
