National Science Day: 'Raman Effect' that won India's 1st Physics Nobel
India observes February 28 as ‘National Science Day’ to mark the discovery of ‘Raman Effect’ by Sir CV Raman on February 28, 1928, the discovery for which he was awarded the Nobel Prize in Physics in 1930. But what exactly is Raman Effect? Let’s try to understand
Rayleigh scattering
Before diving into the Raman Effect, it is important to first understand its background.
It all started with the ‘Rayleigh scattering’, a theory proposed by British physicist Lord Rayleigh, in which he answered the most basic question: Why is the sky blue? His theory stated that when sunlight interacts with air particles, it gets scattered. Because light is made up of different colours, the degree of scattering depends on the wavelength of the colour. Since violet and blue colours have low wavelengths, they get scattered the most. But because human eyes are more sensitive to the blue colour, the sky appears blue.
Rayleigh then argued that the blue colour of the ocean is the mere reflection of the blue colour of the sky. Now, this is where, ‘Bharat Ratna’ Sir CV Raman makes his entry.
Curiosity of Raman
Travelling from London to Bombay, aboard SS Narkunda, Raman became fascinated with the deep blue colour of the Mediterranean. His probing mind didn’t allow him to accept Lord Rayleigh’s explanation of the ocean’s blue colour.
After some research, Raman concluded that the blue colour of the ocean is not the reflection of the sky. It is because of the scattering of light by water molecules. This was not a remarkable discovery since the basic explanation had already been given by Rayleigh. Raman had just replaced ‘scattering by air particles’ to ‘scattering by water molecules’.
Raman Effect
After this, Raman got deeply involved in understanding the ‘interaction’ of light with the particles of liquid from which it is passing, before getting scattered. He used 60 different liquids and passed light through them. All the 60 experiments led to a single result: Some part of the scattered light (typically 0.000001 per cent) contains a different colour (different wavelength) than the original light.
This essentially means that some part of the light is changing its wavelength after interacting with the liquid (this came to be known as Raman Effect). It can only happen when there is a significant interaction between the particles of light (photons) and the molecules present in the liquid, which undergoes an energy exchange.
Foundation for future
Sir CV Raman’s remarkable observation laid the foundation for future studies, particularly in the field of quantum physics, which lays special emphasis on understanding the dynamics of change in the photon’s energy when it interacts with atoms of other molecules.
Prof RW Wood, physicist from John Hopkins University, who initially expressed skepticism towards CV Raman, described Raman Effect as ‘a very beautiful discovery’ and considered it as one of the most convincing proofs of quantum theory.
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