Optics Question 976
Question: The velocity of light in a medium is half its velocity in air. If ray of light emerges from such a medium into air, the angle of incidence, at which it will be totally internally reflected, is
[Roorkee 1999]
Options:
A) $ 15^{o} $
B) $ 30^{o} $
C) $ 45^{o} $
D) $ 60^{o} $
Show Answer
Answer:
Correct Answer: B
Solution:
$ \mu =\frac{c}{v}\Rightarrow \mu =\frac{c}{c/2}=2 $
also for total internal reflection $ i>c\Rightarrow \sin i\ge \sin c\Rightarrow \sin i\ge \frac{1}{\mu } $
Hence $ i\ge {{\sin }^{-1}}( \frac{1}{\mu } ) $ or $ i\ge 30^{o} $
