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
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
