Question

The critical angle of a certain medium is ${\sin }^{-1}\left(\frac{4}{5}\right)$. The polarising angle of medium is

• A. ${\tan }^{-1}\left(\frac{5}{4}\right)$
• B. ${\sin }^{-1}\left(\frac{4}{5}\right)$
• C. ${\sin }^{-1}\left(\frac{5}{4}\right)$
• D. ${\tan }^{-1}\left(\frac{4}{3}\right)$

Answer 1

Answer: (A)

Here, Critical angle, $i_c={\sin }^{-1}\left(\frac{4}{5}\right)$
$\therefore \sin i_c=\frac{4}{5}$
As $\mu =\frac{1}{\sin i_c}=\frac{5}{4}$
According to Brewster's law,
$\tan i_p=\mu$
where, $i_p$ is the polarising angle
$\therefore \tan i_p=\frac{5}{4}$
$\Rightarrow i_p={\tan }^{-1}\left(\frac{5}{4}\right)$