Question

The value of critical angle for material of refractive index $\frac{2\sqrt{3}}{3}$ is:

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

Answer 1

The correct option is B ${60}^{\circ }$

Refractive index of the material is given as:
$\mu =\frac{2\sqrt{3}}{3}$

From the formula of critical angle:
$\sin C=\frac{1}{\mu }=\frac{1}{2\sqrt{3}/3}$
$\sin C=\frac{3}{2\sqrt{3}}=\frac{\sqrt{3}}{2}$
$C={60}^{\circ }$