Plane Polarisation (Edexcel A Level Physics)

Revision Note

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Lindsay Gilmour



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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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.