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Scattering is a general physical process whereby some forms of radiation,
such as light or moving particles, for example, are forced to deviate from a
straight trajectory by one or more localized non-uniformities in the medium
through which it passes.
A large number of molecules are present in the
earth’s atmosphere. These molecules scatter light in various directions. The air is composed of many tiny
particles including dust and water vapour. As the sunlight passes through the
air, the shorter blue light waves are reflected and refracted by the particles
while the other coloured light waves being longer are unaffected and are not
reflected by the water vapour or dust in the air. Blue, therefore, is scattered
the most and this explains the bluish colour of the sky. At sunset or sunrise,
the sunrays have to cover large atmospheric distances to reach us and most of
the blue light gets scattered and doesn’t reach us. The sky as well as the sun,
at sunrise and sunset, therefore looks reddish.
Tyndall Effect The earth’s atmosphere is a heterogeneous
mixture of minute particles. These particles include smoke, tiny water droplets,
suspended particles of dust and molecules of air. When beam of light strikes
such air particles, the path of the beam becomes visible. Similarly the path of
a beam of light passing through a true solution is not visible. However, its
path becomes visible through a colloidal solution where the size of the
particles is relatively larger. The phenomenon of scattering of light by the
colloidal particles gives rise to Tyndall effect.
Tyndall effect is the
visible scattering effect of light on particles along the path of a beam of
light passing through a colloid system.
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