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} $

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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°).



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