Polarization Meaning in Physics| Polarization of light

Polarization in physics?

Polarization is the attribute that wave oscillations have a definite direction relative to the direction of propagation of the wave. EM waves are transverse waves that may be polarized. The direction of polarization is defined to be the direction parallel to the electric field of the EM wave.

Which is the best definition of polarization?

 The action of polarizing or state of being or becoming polarized: such as. a(1) : the action or process of affecting radiation and especially light so that the vibrations of the wave assume a definite form. (2) : the state of radiation affected by this process.

What is the formula of polarization?

Polarization P in its quantitative meaning is the amount of dipole moment p per unit volume V of a polarized material, P = p/V.

Only transverse wave can be polarized but not longitudinal wave. Why?

In longitudinal wave, there is no vibration perpendicular to the direction of propagation of
wave.
Only in transverse wave, vibration is in all possible direction perpendicular to the direction of
propagation of wave.
So, only for transverse wave it is possible to confine vibration along a single direction
perpendicular to the direction of propagation of light, and hence polarized.

Unpolarized and Polarization of Light

Unpolarized Light:

• The wave for which vibrations are not confined only in a single plane contains the
direction of propagation is called unpolarized wave.
• It can be obtained by the ordinary or natural source of light.
• It is denoted by the ray light arrow with bold dot with arrow perpendicular to it.

Polarized Light:

• The wave for which vibrations are confined only in a single plane contains the direction of
propagation is called polarized or plane-polarized wave.
• It can not be obtained by the ordinary source of light.
• It is obtained by the ray light arrow with bold dot or arrow perpendicular to it.

Different between polarized and unpolarized light wave

Polarization of Wave

When unpolarized light passes through the tourmaline crystal, it becomes polarized 𝑖. 𝑒. Wave’s vibration is
confined to a single plane containing direction of propagation.
• Process of formation of polarized wave is called polarization of wave.
• The device used to polarize or analyze the polarized light is called polaroid.
• The polaroid used to produce polarized light from unpolarized light is called polarizer.
• The polaroid used to identify polarized wave is called analyzer

Some polarization method of light:
A) Selective Absorption Method: Here only the wave for which electric vibration is along the axis of transmission is allowed to pass through polaroid and another components are absorbed .
B) Partial Reflection Method: Here only the wave that is reflected from reflecting surface get polarized in a plane parallel to reflecting surface at suitable condition.
C) Polarization by Refraction: Here only the wave that is refracted from calcite crystal like object get polarized at suitable condition.

Polarization of light wave

Applications of Polaroid

Polaroids have several uses

  1. In sunglasses and camera filters: Sunglasses and camera filters are made of polarizing
    sheets to reduce the glare of light produced by reflection from shiny surface such as
    water.
  2. In wind screens: The car head lights and wind screens of motor cars are fitted with
    polaroid films to reduce the headlight and sunlight glares.
  3. In 3-D movies glasses: A polarized 3D system uses polarization glasses to create the
    illusion of three dimensional images by restricting the light that reaches each eye.
  4. In liquid crystal displays (LCD): In many watches, calculators and portable computers,
    LCD is used which works on the basis of principle of polarization to form numbers and
    letters.

Experimental verification of Polarization of Light

Two tourmaline crystals polarizer (P1) and analyses (P2) cut in a plane parallel to their axis are taken along the same line
parallelly.
Light from source is allowed to incidence on P1 perpendicularly on its plane and then to P2.
Intensity of light passing from P2 is maximum only if it’s axis is parallel to axis of P1 and minimum when it is perpendicular.
Since, tourmaline crystal P1
allows to pass only those light wave for which vibration is parallel to its axis of crystal
(transmission axis), experiment shows that light can be polarized and hence light is transverse wave.

Polarization by Reflection

Sir David Brewster observed that light can be polarized by partial reflection.
When beam of ordinary light incidence on the surface of a given transparent medium, the reflected ray is completely plane polarized at particular angle of incidence.
The angle of incidence on transparent object at which reflected ray is completely plane polarized is called Polarizing angle (𝜃𝑝) or Brewster’s angle (𝜃𝐵) .
At this case, angle between the reflected and refracted ray is 900.

Brewster’s law:


Brewster stated that refractive index of the transparent medium is equal to the tangent of angle of polarization to for the medium. This is called Brewster’s law.

Brewster’s law:

𝑖. 𝑒 𝜇 = tan 𝜃𝑝
Here 𝜇 and 𝜃𝑝 are refractive index of reflecting medium and polarizing angle of medium.
Proof:
Unpolarized ray (IO) of light incident on the surface of partially
reflecting surface XY.
At particular angle of incidence 𝑖 = 𝜃𝑝 , reflected ray (OR) is
completely plane polarized and refracted ray (OD) is partially
polarized. Polarized reflected ray (OR) has vibration confined in a
plane parallel to reflecting surface

In this case, reflected ray (OR) and refracted ray (OD) are perpendicular
to each other.
∴ 𝑟 + 𝑖 + 900 = 1800
Here, 𝑖 = 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑐𝑒 = 𝜃𝑝 = 𝑝𝑜𝑙𝑎𝑟𝑖𝑧𝑖𝑛𝑔 𝑎𝑛𝑔𝑙𝑒
and r = 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑟𝑒𝑓𝑟𝑎𝑐𝑡𝑖𝑜�

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