Explain the Phenomenon of polarization
The Phenomenon of interference and diffraction have proved that light has wave nature, but these phenomenon do not show whether light waves are longitudinal or transverse. the phenomenon of polarization shows that light waves are transverse.
In Transverse mechanical waves, the vibration can be oriented along vertical, horizontal or any other direction in each of these caces, the wave is said to be polarized.
The plane of polarization is the plane containing the direction of vibration of the particles of the medium and the direction of propagation of wave.
A light wave produced by osillating charge consists of a periodic variation of electric field vector along with magnetic field vector at right angle to each other.
The direction of polarization in a plane polarized light wave is taken, as the direction of electric field vector.
A beam of ordinary light consisting of large number of planes of vibration is called unpolarized ligh.
The beam of light in which all vibration are confined to a single plane of vibration is called polarized light.
Production and Detection of plane polarized light
The light emitted by an ordinary incandescent bulb is unpolarized, because its vibrations are randomly oriented in space. It is possible to obtain plane polarized beam of light from un polarized light by removing all waves from the beam except those having vibrations aling one particular dirction. This can be achieved by various method as given below:
(1) Selective absorption
(2) Reflection from different surfaces
(3) Scatterting by small particles
(4) Refraction through crystals
Selective absorption method:
Selective abortion method is the most common method to obtain plane polarized light by using certain types of materials called dichroic substance. These transmit only those waves, whose vibration are Fig. Parallel to’ the particular direction and will absorb those waves whose that vibration are in other directions. One such commercial polarizing material is Polaroid.
If the un-polarized light is made incident on thé sheet of Polaroid, the transmitted light will be Blane polarized. If the second sheet of Polaroid is placed I such a way that the axes of the Polaroid, as shown by the straight drawn c them, are parallel, the light, is transmitted through the second Polaroid also.
The second Polaroid is slowly rotated about the beam of light as an axis: o rotation, the light emerging out. of the second Polaroid gets dimmer and dimmer and disappears when the axes become mutually perpendicular. The •Light reappears on-further rotation and becomes brightest when the axes are again parallel to q. each other.
Transverse Nature of Light:
This experiment proves that light-waves are transverse waves. If the light waves were longitudinal/théy; would never disappear. Even if the two Polaroids. were mutually perpendicular. Sunlight also becomes partially polarized because of scattering by air molecules of the Eårth’s atmosphere or by reflection we can obtain the partially polarized light instead of.glare of light.
Reflection from. different surfaces: RefleCtion of light from .water,. Glass, snow and rough road surfaces, for larger angles of incidences, produces glare. Since the reflected -light is partially • polarized, glare can considerably be reduced by using polarized sunglasses. Scattering by small particles: Sunlight also becomes partially polarized due to scattering by air molecules of – earth’s atmosphere.
This effect can be observed by looking directly up through a pair of’ sunglasses made of pqlårizing glass. Certain directions of the lens, less light passes through than at others — Polaroid: A synthétic double refracting substance, that strongly absorbs polarized light in a dry plane, while easily passing polarized light in another plane of right angles.