• Transverse waves can oscillate in any plane perpendicular to the direction of motion (and energy transfer) of the wave
• Such waves are said to be?unpolarised
• Polarisation?occurs when

Particles are only allowed to oscillate in one of the directions perpendicular to the direction of wave propagation

• When a transverse wave is polarised, its?electric field?is only allowed to oscillate in?one fixed plane?perpendicular to the direction of motion of the wave
  • For EM waves it is the?plane?of the?electric fields?oscillation that defines its?plane of polarisation
• ?A transverse wave can be vertically polarised, horizontally polarised, or polarised in any direction in between

Diagram showing the displacement of unpolarised and polarised transverse waves

• Since longitudinal waves oscillate in the same direction as the direction of motion of the wave,?polarisation of longitudinal waves cannot occur

• Methods of polarisation include polarising filters and?reflection from a non-metallic plane surface

Polarising Filters

• Light waves can be polarised by making them pass through a?polarising filter?(also known as a?polariser)
• The filter imposes its plane of polarisation on the incident light wave
• A polariser with a vertical?transmission axis?only allows vertical oscillations to be transmitted through the filter (A)
• If vertically polarised light is incident on a filter with a horizontal transmission axis, no transmission occurs (B), and the wave is blocked completely

Diagram showing an unpolarised and polarised wave travelling through polarisers