A beam of light A O is incident on a glass slab (p = 1 .54) in a direction as shown in fig. (2). The reflected ray OB
 

s passed through a Nicol prism on viewing through a Nicol prism, we find on rotating the prism that

For complete polarisation of reflected light
$$\begin{gathered} \mathrm{\mu }=\tan \mathrm{\varphi }(\mathrm{\varphi }=\text{ Brewster's angle }) \\ \mathrm{\varphi }={\tan }^{-1}\mathrm{\mu }={\tan }^{-1}(1\cdot 54)={57}^{\circ } \\ \mathrm{From} \mathrm{fig}. \left(2\right) \mathrm{angle} \mathrm{of} \mathrm{incidence} \\ ={90}^{\circ }-{33}^{\circ }={57}^{\circ } \end{gathered}$$

Hence the reflected light is completely polarised. .When &e plane polarised light is viewed through a rotating Nicol, the intensity gradually reduces to zero and then again increases