Question

A light wave enters from first medium into second medium. Its velocity in second medium is double of that in first medium. For the phenomenon of total internal reflection to take place, the angle of incidence must be greater than a certain value. This value is

• A. ${90}^0$
• B. ${60}^0$
• C. ${45}^0$
• D. ${30}^0$

Answer 1

The correct option is D ${30}^0$

Given, velocity of light wave doubles in second medium.
Let velocity of light in first medium be $v$

$\therefore$ Velocity of light in second medium $=2v$

Now, $sinC=\frac{\text{Velocity in 1st medium}}{\text{Velocity in 2nd medium}}$

$\therefore \frac{v}{2v}=\frac{1}{2}$

$\Rightarrow C={30}^0$