#### Consider a light beam incident from air to a glass slab at Brewster’s angle, as shown in Fig. 10.1. A Polaroid is placed in the path of the emergent ray at point P and rotated about an axis passing through the centre and perpendicular to the plane of the polaroid.A. For a particular orientation, there shall be darkness as observed through the polaroid. B. The intensity of light, as seen through the polaroid, shall be independent of the rotation. C. The intensity of light, as seen through the polaroid, shall go through a minimum but not zero for two orientations of the polaroid. D. The intensity of light, as seen through the polaroid shall go through a minimum for four orientations of the polaroid.

The answer is the option (c)

Explanation: Brewster’s law states that when a beam of unpolarized light is reflected in a transparent medium, the resultant reflected light is completely polarized at a certain angle of incidence. It is given by:

From the figure, it is clear that

$\theta p \;+ \theta \;r = 90^{\circ}$

Also, $n = \tan \theta \;p$ (Brewster’s law)

$(i) For \;i < \theta \;p \;or\; i > \theta \;p$

Both of the reflected and refracted light ray become partially polarized.

$(ii) For glass\; \theta \;p = 51^{\circ} f\! or \; water\; \theta \;p = 53^{\circ}$