Edexcel International A Level Physics

Revision Notes

2.17 Plane Polarisation

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Plane Polarisation

  • 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

Polarised waves diagram, downloadable AS & A Level Physics revision notes

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

Waves through a polariser, downloadable AS & A Level Physics revision notes

Diagram showing an unpolarised and polarised wave travelling through polarisers

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