Optics Question 982
Question: Light wave enters from medium 1 to medium 2. Its velocity in 2nd medium is double from 1st. For total internal reflection the angle of incidence must be greater than
[CPMT 2002]
Options:
A) $ 30^{o} $
B) $ 60^{o} $
C) $ 45^{o} $
D) $ 90^{o} $
Show Answer
Answer:
Correct Answer: A
Solution:
$ \frac{{\mu _{2}}}{{\mu _{1}}}=\frac{v _{1}}{v _{2}}=\frac{1}{2}\Rightarrow \frac{{\mu _{1}}}{{\mu _{2}}}=2({\mu _{1}}>{\mu _{2}}) $
For total internal reflection $ _{2}{\mu _{1}}=\frac{1}{\sin C}\Rightarrow \frac{{\mu _{1}}}{{\mu _{2}}} $
$ =\frac{1}{\sin C}\Rightarrow 2=\frac{1}{\sin C}\Rightarrow C=30^{o} $
So, for total (Internal reflection angle of incidence must be greater than 30°).
