Polarisation: Plane polarised waves.

TRANSVERSE WAVES ARE POLARISABLE. LONGITUDINAL WAVES ARE NOT. (vibration in the same plane as difrection of propogation)

Here is an unpolarised wave.
It has many planes of disturbance.
They are all perpendicular to the direction of propogation, at any angle around the axis.

Here is a Polarised wave.

It has ONE plane if disturbance, perpendicular to the direction of trave, at ONE angle about the axis.

Note: For EM waves, we consider the E field when describing the plane of polarisation.

Some waves are generated as polarised waves, and others can be polarised.

Rotating the metal rods through 90 degrees causes the probe not to pick up any microwaves since none are geting through the rods as the generator generates polarised waves.

Rotating the probe through 90 degrees would have the same effect, none would still be recieved.



Light from lightbulbs is not polarised as it relies on random excitement of electrons, rather than specific motions of electrons. Light can be polarised using a polaroid.


Applications.

SUNGLASSES - reduce glare. Reflected rays from shiny surfaces are polarised. Sunglasses are intended to absorb the radiation

OPTICAL ACTIVITY - some solutions rotate plane of disturbance. Different concentrations affect this by different amounts.

STRESS ANALYSIS - Clear plastic models are made of structures which are placed between polaroids, stressed, and stress patterns observed.
LCD DISPLAYS - Polarised light passes through the liquid crystal and is rotated by 90 degrees. It is reflected and is re-rotated. A PD across areas of the liquid reduces the roration, thus no light can get through, causing the dark patches.