CBSE Class 12 · 2013 · Wave OpticsShort Answer

(a) $\text{Linearly polarized light}$ is light in which the electric-field vibrations are confined to a single direction perpendicular to the direction of propagation.
When unpolarized sunlight passes through a polaroid, the long-chain molecules absorb the field component parallel to the molecular alignment and transmit only the perpendicular component, so the emerging light is linearly polarized (a polaroid selects one plane of vibration).
(b) When unpolarized light of intensity $I_0$ falls on a single polaroid, the transmitted intensity is

and this value is $\text{independent of the orientation}$ of the polaroid. Hence on rotating the polaroid the transmitted intensity remains constant at $\frac{I_0}{2}$.