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Definition: Raman, Sir Chandrasekhara Venkata from Philip's Encyclopedia

Indian physicist. He greatly influenced the growth of science in India, and founded (1946) the Raman Institute. Raman received the 1930 Nobel Prize in physics for his research on the diffusion of light and his discovery of the Raman effect. This states that there is a slight change in the frequency of monochromatic (single-wavelength) light that has been scattered by passing through a transparent material. This effect appears as secondary spectral lines on each side of the primary spectral line. See also quantum theory; scattering

Summary Article: Raman, Chandrasekhara Venkata (1888-1970)
from The Hutchinson Dictionary of Scientific Biography

Place: India

Subject: biography, physics

Indian physicist who discovered that light is scattered by the molecules in a gas, liquid, or solid so as to cause a change in its wavelength. This effect is known as Raman scattering and the Raman spectra produced are used to obtain information on the structure of molecules. For its discovery, Raman was awarded the 1930 Nobel Prize for Physics.

Raman was born in Trichinopoly in Madras (now Tiruchchirappalli in Tamil Nadu) on 7 November 1888. He studied at the AVN College in Vizagapatam, where his father was professor of mathematics and physics, and at the Presidency College of the University of Madras where he obtained a BA in 1904 and an MA in 1907. Although aged only 16 and 19 respectively, Raman gained first-class degrees of great distinction. However, he was unable to continue his scientific education as this would have meant leaving India, and because there were no opportunities for a scientific career in India, Raman entered the financial division of the civil service in 1907, working as an accountant in Calcutta (now Kolkata) for ten years.

During this time, Raman pursued his studies privately, using the facilities at the laboratories of the Indian Association for the Cultivation of Science in Calcutta. He concentrated his efforts on investigations into vibration in sound and the theory of musical instruments, an interest that continued throughout his life. His work on these subjects and on diffraction prompted an offer of the professorship of physics at the University of Calcutta, which Raman took up in 1917.

Raman remained at Calcutta until 1933, and it was during this period of his life that he made the discovery that was his most important contributions to physics. In 1926 he established the Indian Journal of Physics and in 1928 was made president of the Indian Science Congress. Further honours came with the award of a knighthood by the British government in 1929 and the Hughes Medal of the Royal Society in 1930, in addition to the Nobel Prize for Physics in the same year.

In 1934, Raman became head of the physics department at the Indian Institute of Science, a post he held until 1948, also serving as president of the Institute 1933-37. The Indian government then built the Raman Research Institute for him at Bangalore and he became its first director in 1948. Raman took his duties as an educator very seriously and trained a great number of young scientists who later rose to positions of responsibility in science. Among his colleagues at the Institute was Homi Bhabha. Raman remained director of his institute until he died in Bangalore on 21 November 1970.

Raman was inspired to work on the scattering of light in 1921, when returning to India by sea from a conference in the UK. He was struck by the intense blue colour of the Mediterranean, which he could not reconcile with the explanation put forward by Lord Rayleigh that attributed the blue colour to the scattering of light by particles suspended in the water. Raman began to investigate this phenomenon upon his arrival in Calcutta. He showed that the blue colour of the sea is produced by the scattering of light by water molecules.

In 1923, Arthur Compton discovered the Compton effect, in which X-rays are scattered on passing through matter and emerge with a longer wavelength. This was explained by assuming that X-ray particles or photons had collided with electrons and lost some energy. In 1925, Werner Heisenberg predicted that this effect should be observed with visible light. Raman had already come to the same conclusion independently and had in fact made a preliminary observation of this light-scattering effect in 1923. He then refined his experiments and in 1928 was able to report the existence of the scattering effect for monochromatic light in dust-free air and pure liquids. The Raman spectra produced show lines displaced to either side of the normal line in a gas and a continuous band in dense liquids. The effect is caused by the internal motion of the molecules encountered, which may impart energy to the light photons or absorb energy in the resulting collisions. Raman scattering therefore gives precise information on the motion and shape of molecules.

Raman's other researches included the effects of sound waves on the scattering of light in 1935 and 1936; he vibration of atoms in crystals in the 1940s; the optics of gemstones, particularly diamonds, and of minerals in the 1950s; and the physiology of human colour vision in the 1960s.

Raman's discovery is important not only because it affords a method for the analysis of molecular structure but also because in demonstrating conclusively that light may behave as particles (photons), it confirms the quantum theory. However Raman is also to be remembered as a pioneer of Indian science.

© RM, 2018. All rights reserved.

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