Question

When the angle of incidence is ${60}^{\circ }$ on the surface of a glass slab, it is found that the reflected ray is completely polarized. The velocity of light in glass is,

• A. $\sqrt{2}\times {10}^8{\text{ms}}^{-1}$
• B. $\sqrt{3}\times {10}^8{\text{ms}}^{-1}$
• C. $2\times {10}^8{\text{ms}}^{-1}$
• D. $3\times {10}^8{\text{ms}}^{-1}$

Answer 1

The correct option is B $\sqrt{3}\times {10}^8{\text{ms}}^{-1}$

As reflected light is completely polarized, therefore,
$i_p={60}^{\circ }$

According to Brewster's law,
$\mu =\tan i_p=\tan {60}^{\circ }=\sqrt{3}$

As, $\mu =\frac{c_a}{c_g}\Rightarrow c_g=\frac{c_a}{\mu }$

$\therefore c_g=\frac{3\times {10}^8}{\sqrt{3}}=\sqrt{3}\times {10}^8{\text{ms}}^{-1}$

Hence, $\left(B\right)$ is the correct answer.