KERALA UNIVERSITY COLLEGE OF TEACHER EDUCATION

KOLLAM

SCATTERING OF LIGHT

SCATTERING OF LIGHT

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.

When light passes through a substance or gas, a part of it

is absorbed and the rest scattered away. The basic

process in scattering is absorption of light by the

molecules followed by re-radiation in different directions.

The strength of scattering can be measured by the loss of

energy in the light beam as it passes through the

medium. In absorption the light energy is converted into

the internal energy of the medium and in scattering the

light energy is radiated in other directions. The strength of

scattering depends on the size of the particle causing

the scattering and the wavelength of light. The scattering

is proportional to 1/h4. This is known as Raleigh's law of

scattering. So the red light is scattered the least and the

violet is scattered the most. This explains why red signals

are used to indicate danger.

BLUE COLOUR OF SKY

The blue color of the sky is due to Rayleigh

scattering. blue sky As light moves through the

atmosphere, most of the longer wavelengths pass

straight through. Little of the red, orange and

yellow light is affected by the air.

However, much of the shorter wavelength light is

absorbed by the gas molecules. The absorbed

blue light is then radiated in different directions. It

gets scattered all around the sky. Whichever

direction we look, some of this scattered blue

light reaches to us. Since we see the blue light

from everywhere overhead, the sky looks blue.

YELLOW COLOUR OF SUN

SUN IS YELLOW DURING SUNSET AND SUN RISE

• After the much of the blue portion of the white light spectrum is absorbed by the molecules in the atmosphere, the rest of the spectrum continues on its journey. Because the blue element has been removed from the spectrum, the remaining components combine to appear yellow or golden to the naked eye.

WHITE COLOUR OF CLOUDS

Clouds appear white because the light coming from the sun has to pass through the water droplets and ice crystals or we can say

that the seven colors of visible spectrum (red, orange, yellow, green, blue, indigo, violet) which when combines forms white

light and this process of combining is done by water droplets or ice crystals present in the clouds. On the whole we can say that

light is reflected in many ways which combines to give white color.