What is Scattering of Light and its Types?

SCATTERING OF LIGHT

When sunlight enters the Earth’s atmosphere, the atoms and molecules of different gases present in the atmosphere refract light in all possible directions.
This is called as ‘Scattering of light’.
In this phenomenon, the beam of light is redirected in all directions when it interacts with a particle of the medium.
The interacting particle of the medium is called as ‘scatterer’.

Types of scattering

When a beam of light, interacts with a constituent particle of the medium, it undergoes many kinds of scattering.
Based on the initial and final energy of the light beam, scattering can be classified as,

Elastic scattering

If the energy of the incident beam of light and the scattered beam of light are the same, then it is called as ‘elastic scattering’.

Inelastic scattering

If the energy of the incident beam of light and the scattered beam of light are not the same, then it is called as ‘inelastic scattering.
The nature and size of the scatterer result in different types of scattering.

They are

- - Rayleigh scattering
  - Mie scattering
  - Tyndall scattering
  - Raman scattering

Rayleigh scattering

The scattering of sunlight by the atoms or molecules of the gases in the earth’s atmosphere is known as Rayleigh scattering.

Rayleigh’s scattering law

Rayleigh’s scattering law states that “The amount of scattering of light is inversely proportional to the fourth power of its wavelength”.
Amount of scattering ‘S’ According to this law, the shorter wavelength colours are scattered much more than the longer wavelength colours.
When sunlight passes through the atmosphere, the blue colour (shorter wavelength) is scattered to a greater extent than the red colour (longer wavelength). This scattering causes the sky to appear in blue colour.
At sunrise and sunset, the light rays from the Sun have to travel a larger distance in the atmosphere than at noon.
Hence, most of the blue lights are scattered away and only the red light which gets least scattered reaches us.
Therefore, the colour of the Sun is red at sunrise and sunset.

Mie scattering

Mie scattering takes place when the diameter of the scatterer is similar to or larger than the wavelength of the incident light.
It is also an elastic scattering. The amount of scattering is independent of wavelength.
Mie scattering is caused by pollen, dust, smoke, water droplets, and other particles in the lower portion of the atmosphere.
Mie scattering is responsible for the white appearance of the clouds.
When white light falls on the water drop, all the colours are equally scattered which together form the white light.

Tyndall Scattering

When a beam of sunlight, enters a dusty room through a window, then its path becomes visible to us.
This is because the tiny dust particles present in the air of the room scatter the beam of light. This is an example of Tyndall Scattering
The scattering of light rays by the colloidal particles in the colloidal solution is called Tyndall Scattering or Tyndall Effect.

Raman scattering

When a parallel beam of monochromatic (single coloured) light passes through a gas or liquid or transparent solid, a part of the light rays is scattered.
The scattered light contains some additional frequencies (or wavelengths) other than that of incident frequency (or wavelength).
This is known as Raman scattering or Raman Effect.
Raman Scattering is defined as “The interaction of light rays with the particles of pure liquids or transparent solids, which leads to a change in wavelength or frequency.”
The spectral lines having a frequency equal to the incident ray frequency are called ‘Rayleigh lines and the spectral lines which are having frequencies other than the incident ray frequency are called ‘Raman lines.
The lines having frequencies lower than the incident frequency are called stokes lines and the lines having frequencies higher than the incident frequency are called Antistokes lines.

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