A level revision

Polarisation of waves

Transverse waves can be polarised that is that the waves vibrate all in the same direction or 'plane'.

When thinking about polarisation you need to remember that a wave is 3d, despite what is usually shown in graphs and diagrams. A wave is free to oscillate in any direction:

The oscillations of the wave may move straight up and down along with the y axis.

Or they may move left and right along with the x axis.

Or anywhere in between.

In an unpolarised wave the oscillations move in all directions:

The wave below is polarised, the oscillations are fixed in a single direction or 'plane' (the y plane in this example)

Evidence of the polarisation of waves can be found by looking at reflected light from a shiny transparent surface, like glass, through a polarising filter, such as a pair of polarising sunglasses. Rotating the filter around shows that, at some angles, the light is reduced or even completely eliminated which shows that the oscillations of the light are travelling in the same direction at that angle and so are all 'absorbed' by the filter.