The atmosphere of earth is full of
particles or molecules like N2, O2, O3, H2, H2O, dust particles etc. These are
so small that we cannot see them with naked eyes. Even with powerful microscope
of 100X or higher available in school labs, air particles are not visible (except
dust particles). When sunlight encounters these particles there is a change in
the direction of sun rays which lead to a phenomenon known as scattering of
light.The sunlight consists of
different frequencies from 430 – 770 THz (or wavelengths 390 -700 nanomoetres).
The colour of the scattered light depends upon the size of the encountered particles.
The process of selective scattering is known as Rayleigh scattering.
The size of the air particles has
size comparable to the wavelength of visible light at the blue end. These
particles are more suitable in scattering light of blue and violet colours as
compared to red colour. This is the reason why sky appears blue in colour. Due to pollution, large size
particles are introduced in the atmosphere. These particles are efficient in
scattering light of longer wavelengths also. This causes the pale blue or grey
colour of the sky in a polluted atmosphere. Watch the video shown below on youtube. This video shows how a laser light is scattered by water and talcom powder. The scattering of laser by water or talcom powder makes its path visible (known as Tyndall's effect) and this property can be used to study relection or refraction.
