vibrations are in one direction perpendicular to direction of propagation/ energy transfer
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A polarised wave oscillates in only one plane (e.g only up and down if vertically polarised), only transverse waves can be polarised. Polarisation provides evidence for the nature of transverse waves because polarisation can only occur if a wave's oscillations are perpendicular to its direction of travel (as they are in transverse waves).
The intensity of a wave is affected by polarisation. As the process of passing through a polarising filter excludes waves of certain orientations, the intensity of the wave after filtering is always less than or equal to its intensity before.