Polarisation is the process through which the oscillations of waves are made to move in one plane only.
The transverse waves are mechanical and they can oscillate in any direction and any orientation which is perpendicular to the direction in which they travel. They are known to be polarised only when the direction of the propagation of wave and the displacement of particles is in a plane.
Longitudinal waves can never be polarised since those waves have particles that vibrate back and forth on the line of propagation and a plane cannot be specified by those two parallel lines.
Polarisation of waves can be done by various techniques.
- By using a Polaroid filter: One such technique is by using a filter. The Polaroid filters are made in such a way that they can block one plane of vibration of the electromagnetic waves. Whenever an unpolarised light is passed through the filter, it comes out with half of its intensity and with the vibrations occurring in a single plane, resulting in it to become a polarised light.
- By Reflection: The unpolarised light can get polarised by reflection off of the non-metallic surfaces. The level of polarisation depends on the angle of light upon the material and also the material that the surface is made up of. The metallic surfaces fail to polarise the light as they reflect light in various directions. But, non-metallic surfaces reflect light in such a way that the reflected light often vibrates in a plane that is parallel to the surface, causing them to get polarised.
- By Refraction: Refraction is a phenomena caused to the movement of a beam of light from one material to another, causing a change in the direction. The refracted light manages to attain some kind of polarisation.
- By Scattering: When the light falls on a surface, it causes the electrons of the material to vibrate, causing an electromagnetic wave radiation in all directions. The new waves collide with neighbouring atoms and force the electrons to vibrate and create another electromagnetic wave. The absorption and the re-emission of light waves cause the scattering in the medium. The scattered light is partially polarised.
APPLICATIONS OF POLARISATION
- Polaroid glasses are used to reduce the amount of light that is approachable to eye.
- Polarisation is useful in receiving and transmitting wave signals. There has to be an aerial alignment of the polarised waves in the plane in order for them to be able to receive maximum signal.
- Laser is an outcome of polarisation of waves.
- 3D movies are possible because of polarisation of light.