Polarisation

Polarisation is when we take an unpolarised transverse wave and ‘filter’ it such that the oscillations (vibrations) only occur in a single plane.

This can be useful, see uses of polarisation.

How do we polarise waves?

Unpolarised waves have oscillations occurring in all sorts of directions. We only want to ‘let through’ one of those directions, so we need some way of filtering out the other directions.

To do that, it’s actually quite simple - we just create a ‘slot’ for the wave that is oscillating in the desired direction to pass through, while blocking the other directions.

For example, if we want to polarise a wave so that the oscillations occur in the vertical direction, we can create a vertical ‘slot’ for the wave to pass through. Then, waves oscillating in the horizontal direction (or any other direction) will be blocked.

What waves can be polarised?

We can only polarise transverse waves - not longitudinal waves.

That’s because the wave oscillations of transverse waves can be fixed to a plane (direction) - but longitudinal waves can’t.

Polaroid

See polaroid.