Chapter: 10th Science : Chapter 2 : Optics
Types of scattering of Light
Types
of scattering of Light
SCATTERING OF LIGHT
When sunlight enters the
Earth’s atmosphere, the atoms and molecules of different gases present in the
atmosphere refract the 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 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 initial and final energy of the light beam, scattering can
be classified as,
1) Elastic scattering 2)
Inelastic scattering
1) Elastic scattering
If the energy of the
incident beam of light and the scattered beam of light are same, then it is
called as ‘elastic scattering’.
2) Inelastic scattering
If the energy of the
incident beam of light and the scattered beam of light are not same, then it is
called as ‘inelastic scattering’. The nature and size of the scatterer results
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’ ∝ 1/λ4
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 wave length.
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 into 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 light rays are 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 ray with the particles of pure liquids or
transparent solids, which leads to a change in wavelength or frequency.”
The spectral lines
having frequency equal to the incident ray frequency is called ‘Rayleigh line’
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 is called stokes lines and the lines having frequencies
higher than the incident frequency are called Antistokes lines.
You will study more
about Raman Effect in higher classes.
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