Polarisation — common mistakes

Be careful when applying Malus' Law! It specifically applies to plane-polarised light passing through a filter. If the initial light source is unpolarised and passes through the first polarising filter, its intensity is typically halved before Malus' Law is used for any subsequent filters.

Polarised sunglasses have vertically aligned transmission axes. This orientation blocks horizontally polarised light, which is a major component of glare caused by reflections off horizontal surfaces like water, snow, or roads, effectively reducing eye strain.

An unpolarised wave oscillates in all possible planes perpendicular to its direction of travel simultaneously. In contrast, a plane-polarised wave has its oscillations restricted to only one specific plane, usually after passing through a polarising filter.

No, sound waves cannot be polarised. This is because sound waves are longitudinal waves, meaning their oscillations are inherently parallel to their direction of energy transfer. There is no 'plane' of oscillation perpendicular to their travel to restrict, unlike transverse waves.