beam, scattering can be classified as, ) Elastic scattering ) Inelastic scattering ) 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’. ) 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’ ∝ λ 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. Optics