Question

A triangular prism of glass is shown in the figure. A ray incident normally to the one face is totally reflected if $\theta$ is ${45}^{\circ }.$ The refractive index of glass is:

• A. $\mu <1.41$
• B. $\mu =1.41$
• C. $\mu >1.41$
• D. None

Answer 1

The correct option is C $\mu >1.41$

For total internal reflection,
incident angle $>$ Critical angle

It means, $\sin \theta >\sin C$

$\Rightarrow \sin \theta >\frac{1}{\mu }$

$\Rightarrow \mu >\frac{1}{\sin \theta }$

$\Rightarrow \mu >\frac{1}{\sin {45}^{\circ }}$

$\therefore \mu >1.41$