Polarisation

Polarisation is the phenomenon of restricting the vibrations of light (its electric or, equivalently, magnetic field vector -- this chapter only discusses the electric field) to one particular direction, perpendicular to the direction the wave propagates in. The phenomena of interference and diffraction demonstrated that light propagates as a wave, but could not by themselves determine whether that wave is transverse or longitudinal, since both types of wave can show interference and diffraction. Polarisation, however, is only possible for a transverse wa …