Question

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

• A. Less than 1.41
• B. Equal to 1.41
• C. Greater than 1.41
• D. None of the above

Answer 1

Answer: (C)

For total internal reflection $\theta > C$
$\Rightarrow \sin \theta > \sin C \Rightarrow \sin \theta > \frac{1}{\mu}$
or $\mu>\frac{1}{\sin \theta} $
$\Rightarrow \mu > \frac{1}{\sin 45^{\circ}} $
$\Rightarrow \mu>\sqrt{2} $
$\Rightarrow \mu > 1.41$