A wave in which the plane of vibration is constantly changing is called an unpolarised wave.
However if the vibrations of a transverse wave are in one plane only then the wave is said to be plane polarised.
When light is plane-polarised the vibrations are made to occur in one plane only.
Light is a transverse electromagnetic wave with the vibrations of an electric and a magnetic field occurring at right angles to each other and in any plane at right angles to the direction of travel of the light.
It is important to realise that transverse waves can be polarised while longitudinal waves cannot.
The fact that light can be polarised means that it is a transverse wave.
| Polarisation with light | |
| Sunglasses | Car windscreens |
| Glare/shine off roads | Optical activity |
| Scattered sunlight | Stresses in materials |
| Liquid crystal displays | '3D' glasses in a cinema |