A polaroid consists of long chain molecules aligned in a
particular direction The electric vectors (associated with the propagating
light wave) along the direction of the aligned molecules get absorbed Thus, if an unpolarised light wave is incident on such a polaroid then
the light wave will get linearly polarised with the electric vector oscillating
along a direction perpendicular to the aligned molecules; this direction
is known as the pass-axis of the polaroid Thus, if the light from an ordinary source (like a sodium lamp) passes
through a polaroid sheet P1, it is observed that its intensity is reduced by
half