POLARISING FILTERS: work by selectively absorbing visible light (or other forms of electromagnetic radiation) whose electrical component lies parallel to conducting elements in the filter. The upper light wave is shown with its electrical component (yellow undulation) oriented vertically. As it passes through the filter it causes electrons to move (illustrated as a little oscillating light in the pale blue column of the filter). In so doing, the electrons absorb energy from the wave and so stop it from passing through. The vertically polarized light is absorbed by the filter. In contrast, the lower wave has its electrical component oriented horizontally. Since the electrons cannot move horizontally they do not absorb energy from the wave and it passes straight through the polarizing filter. Filters can be metal wires or molecules (in huge arrays) oriented in such a way that electrons can move in one direction. For example, microwaves can be selectively absorbed by a metal grille. This induced movement of electrons in a conductor by an electromagnetic wave is how radio waves are absorbed by an antenna.
POLARIZING FILTERS: are used in sunglasses to reduce glare since most reflected light bounces off horizontal surfaces and is thereby polarized horizontally (e.g. reflection from the sea or the surface of a pool). Polarising filters are used in photography for similar reasons. In microscopy they can supply polarised light which is then passed through the object. Changes in the polarization brought about by the object are then made obvious by inspection through a second polarizing filter.