Question

Why does unpolarized light from a source show a variation in intensity when viewed through a polaroid
which is rotated

Answer 1

A polaroid consists of long chain molecules. aligned in a particular direction. The electric vectors along the direction of aligned molecules get absorbed. Thus if the unpolarised light from a source passes through a polaroid, its intensity is reduced by half. Rotating the polaroid has no effect on the transmitted beam and transmitted. intensity remains constant.