Consider a light beam incident from air to a glass slab at Brewster’s angle as shown in Fig
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

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The intensity of light as seen through the polaroid shall be independent of the rotation

For a particular orientation, there shall be darkness as observed through the Polaroid

The intensity of light as seen through the Polaroid shall go through a minimum but not zero for two orientations of the Polaroid

The intensity of light as seen through the Polaroid shall go through a minimum for four orientations of the Polaroid

answer is C.

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Detailed Solution

According to Brewster's law, the light reflected from the top of the glass slab gets polarised as shown in the figure. The light refracted into the glass slab and the light emerging from the glass slab is only partially polarised.
Therefore, when a polaroid is held in the path of emergent light P, and rotated about an axis passing through the centre and perpendicular to the plane of polaroid, the intensity of light shall go through a minimum but not zero for two orientations of the polaroid.

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