C.V. Raman

                                                                    C.V. Raman (1888-1970)

Chandra shekhar  Venkat Raman is the only Indian naational to receive Nobel prize (1930) in physics till date. His love for physics was so intensse that he resigned his job of an officer in Indian finance department and accepted the post of Palit Professor of Physocs at the Department of Physocs, Calcutta University. His main contributions are : Raman effect on scattering of light, molecular diffraction of light, mechanical theory of bowed strings, diffraction of X-rays, theory of musical instruments and physics of crystals.
As Director of Indian Institute of Science, Bangalore and later as the founder Director of Raman Research Institute, he did yeoman's to Indian science and put it on firm footings in pra-independence period.
1. Blue Colour of the Sky: we know that scattering of light by air molecules, water droplets or dust particles present in the atmosphere can be explained in accordance with Rayleigh's law. The shorter wavelengths are sscattered more than the longer wavelengths. Thus, the blue light is scattered almost six times more intensely than the red light as the wavelength of the blue light is roughly 0.7 time that of the red. the scattered light becomes rich in the shorter wavelengths of violet, blue and green colours. On further scattering , the violet light does not feach observe's eye as the eye is compartatively less sensitive to violet then blue and other wavelengths in its neighbourhood. So when we look at the sky far away from the sun, it appears blue.
2. White colour of the clouds: the clouds are formed by the assembly of small water drops whose sixe becomes more than the average wavelength of the visiible light (5000A). These droplets scatter all the wavelengths with almost equal intensity. The resultant scattered light is therefore white. So, a thin layer of clouds appears white.

3. Red colour of the sun at sunrise and Sunset: we are now able to understand the red colour of the sun at sunrise and sunset. In the morning and evening when the Sun is near the horizon, light has to travel a greater distance through the atomosphere. The violet and blue wavelengths are scattered by dust particles and air molecules at and angle of About 90⁰ . Thesunlight thus becomes devoid of shorter wavelengths and the longer wavelenght of red colour reaches the observer. so the sun appears to us as red.