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(Image Courtesy : http://www.photonics.cusat.edu/Article5.html)

Feb 28th is our National Science day ! This day, in the year 1928, C.V. Raman announced to the world his famous discovery, a discovery which would earn him a Nobel prize. You can read about his work in the presentation speech that preceded his nobel lecture. Some excerpts:

The diffusion of light is an optical phenomenon, which has been known for a long time. A ray of light is not perceptible unless it strikes the eye directly. If, however, a bundle of rays of light traverses a medium in which extremely fine dust is present, the ray of light will scatter to the sides and the path of the ray through the medium will be discernible from the side. We can represent the course of events in this way; the small particles of dust begin to oscillate owing to electric influence from the ray of light, and they form centres from which light is disseminated in all directions. The wavelength, or the number of oscillations per second, in the light thus diffused is here the same as in the original ray of light. But this effect has different degrees of strength for light with different wavelengths. It is stronger for the short wavelengths than for the long ones, and consequently it is stronger for the blue part of the spectrum than for the red part. Hence if a ray of light containing all the colours of the spectrum passes through a medium, the yellow and the red rays will pass through the medium without appreciable scattering, whereas the blue rays will be scattered to the sides. This effect has received the name of the “Tyndall effect”.

Lord Rayleigh, who has made a study of this effect, has put forward the hypothesis that the blue colours of the sky and the reddish colouring that is observed at sunrise and sunset is caused by the diffusion of light owing to the fine dust or the particles of water in the atmosphere. The blue light from the sky would thus be light-scattered to the sides, while the reddish light would be light that passes through the lower layers of the atmosphere and which has become impoverished in blue rays owing to scattering. Later, in 1899, Rayleigh threw out the suggestion that the phenomenon in question might be due to the fact that the molecules of air themselves exercised a scattering effect on the rays of light.

In 1914 Cabannes succeeded in showing experimentally that pure and dustless gases also have the capacity of scattering rays of light.

But a closer examination of scattering in different substances in solid, liquid, or gaseous form showed that the scattered light did not in certain respects exactly follow the laws which, according to calculation, should hold good for the Tyndall effect. The hypothesis which formed the basis of this effect would seem to involve, amongst other things, that the rays scattered to the sides were polarized. This, however, did not prove to be exactly the case.

This divergence from what was to be expected was made the starting point of a searching study of the nature of scattered light, in which study Raman was one of those who took an active part. Raman sought to find the explanation of the anomalies in asymmetry observed in the molecules. During these studies of his in the phenomenon of scattering, Raman made, in 1928, the unexpected and highly surprising discovery that the scattered light showed not only the radiation that derived from the primary light but also a radiation that contained other wavelengths, which were foreign to the primary light.

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(Image Courtesy : http://www.photonics.cusat.edu/Article5.html)

The National Science day speech of President of India is available here. He starts off with

My greetings to all of you. I am indeed very happy to talk to you on the occasion of National Science Day, which is celebrated on the 28th of February every year, the day in the year 1930, Nobel Laureate Sir CV Raman announced a landmark discovery which is finding applications today in the area of continuous wave all-silicon laser. On this day, the nation pays tribute and expresses its gratitude to all the scientists who have made our dream of using the science and scientific discoveries as vehicles for economic development, a reality. Celebration of Science will attract many young children to take up science as a career. This is the day, our Scientists may like to rededicate themselves to create high quality scientific research output from India and make the nation proud. Science day is the day to remind us that the important ingredient for societal transformation would mainly come from science.

and then goes on to talk about the usual pet topics which are so dear to him – Solar cells and other alternatives that are being explored in energy research. No pure science here though 😦 which in a way is what I expected ..

Indian science, in my opinion, is at crossroads. There is a lot which remains to be done – many tasks waiting for scientists of different hues and world views to take them up. And India with its diversity and intellectual potential has no excuse for not getting them done. To quote the concluding words of this years budget speech,

The young people of India are building castles, it may appear that those castles are in the air, but as Henry David Thoreau said: “If you have built castles in the air, your work need not be lost; that is where they should be. Now put the foundations under them.” It is our duty to put the foundations on which the young can build their castles.

(via nanopolitan )

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