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  4. Consider a light beam incident from air to a glass slab at Brewster's angle as shown in figure. 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. <img class=img-fluid question-image alt=image src=https://cdn.tardigrade.in/img/question/physics/75a2ebc1d69210ae742f0cf99db43e9e-.png />

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Q. Consider a light beam incident from air to a glass slab at Brewster's angle as shown in figure. 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.
image

Wave Optics

Solution:

According to Brewsters law, the light reflected from the top of glass slab gets polarised as shown in figure.
image
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 at $P$, and rotated about an axis passing through the centre and perpendicular to plane of polaroid, the intensity of light shall go through a minimum but not zero for two orientations of the polaroid.