Question

How does a Polaroid work (not a Polaroid camera)?

Answer 1

Generally, light waves are unpolarized as they are composed of many waves with all possible directions of polarization. Polaroids are composed of long molecules aligned in one direction (polarization axis). This polarization axis only allows vibrations of the EM wave that are parallel to the axis to pass through. Any vibrations that are perpendicular to the polarization axis are blocked by the polaroid. So polaroids act as a polarizing slit for light, allowing only polarization in one direction to pass through. This ability to reduce the intensity of light is the primary use of Polaroid. For example, Polaroids are used on spectacles to reduce glare.