Albert Einstein (1879-1955)
Albert Einstein, born in Ulm, Germany in 1879, is universally regarded as one of the greatest physicists of all time. His astonishing scientific career
began with the publication of three path-breaking papers in 1905. In the
first paper, he introduced the notion of light quanta (now called photons)
and used it to explain the features of photoelectric effect that the classical
wave theory of radiation could not account for. In the second paper, he
developed a theory of Brownian motion that was confirmed experimentally a few years later and provided a convincing evidence of the atomic picture of matter. The third paper gave birth to the special theory of relativity that made Einstein a legend in his own life time. In the next decade, he explored theconsequences of his new theory which included, among other things, the mass-energy equivalence enshrined in his famous
equation E = mc2. He also created the general version of relativity (The General Theory of Relativity),
which is the modern theory of gravitation. Some of Einstein’s most significant later contributions are:
the notion of stimulated emission introduced in an alternative derivation of Planck’s blackbody radiation
law, static model of the universe which started modern cosmology, quantum statistics of a gas of massive bosons, and a critical analysis of the foundations of quantum mechanics. The year 2005 was declared as International Year of Physics, in recognition of Einstein’s monumental contribution to physics, in year 1905, describing revolutionary scientific ideas that have since influenced all of modern.
Satyendranath Bose (1894-1974)
Satyendranath Bose, born in Calcutta in 1894, is among the great Indian physicists who made a fundamental contribution to the advance of science
in the twentieth century. An outstanding student throughout, Bose started
his career in 1916 as a lecturer in physics in Calcutta University; five years later he joined Dacca University. Here in 1924, in a brilliant flash of insight, Bose gave a new derivation of Planck’s law, treating radiation as a gas of photons and employing new statistical methods of counting of photon states.
He wrote a short paper on the subject and sent it to Einstein who
immediately recognised its great significance, translated it in German and forwarded it for publication. Einstein then applied the same method to a gas of molecules.
The key new conceptual ingredient in Bose’s work was that the particles were regarded as indistinguishable, a radical departure from the assumption that underlies the classical Maxwell- Boltzmann statistics. It was soon realised that the new Bose-Einstein statistics was applicable to particles with integers spins, and a new quantum statistics (Fermi-Dirac statistics) was needed for particles with half integers spins satisfying Pauli’s exclusion principle. Particles with integers spins are now known as bosons in honour of Bose.
An important consequence of Bose-Einstein statistics is that a gas of molecules below a certain temperature will undergo a phase transition to a state where a large fraction of atoms populate the
same lowest energy state. Some seventy years were to pass before the pioneering ideas of Bose, developed
further by Einstein, were dramatically confirmed in the observation of a new state of matter in a dilute gas of ultra cold alkali atoms - the Bose-Eintein condensate.Sir C.V. Raman(1888-1970)
Chandrashekhara Venkata Raman was born on 07 Nov 1888 in Thiruvanaikkaval.
He finished his schooling by the age of eleven. He graduated from Presidency
College, Madras. After finishing his education he joined financial services of the Indian Government.
While in Kolkata, he started working on his area of interest at Indian Asso-
ciation for Cultivation of Science founded by Dr. Mahendra Lal Sirkar, during his evening hours. His area of interest included vibrations, variety of musical instruments, ultrasonics, diffraction and so on.
In 1917 he was offered Professorship at Calcutta University. In 1924 he was
elected ‘Fellow’ of the Royal Society of London and received Nobel prize in Physics in 1930 for his discovery, now known as Raman Effect.
The Raman Effect deals with scattering of light by molecules of a medium when they are excited to vibrational energy levels. This work opened totally new avenues for research for years to come.
He spent his later years at Bangalore, first at Indian Institute of Science and then at Raman Research Institute. His work has inspired generation of young students.Conservation laws in physics
Conservation of energy, momentum, angular momentum, charge, etc are considered to be fundamental laws in physics. At this moment, there are many such conservation laws. Apart from the above four, there are others which mostly deal with quantities which have been introduced in
nuclear and particle physics. Some of the conserved quantities are called spin, baryon number, strangeness, hypercharge, etc, but you need not worry about them.
A conservation law is a hypothesis, based on observations and experiments. It is important to
remember that a conservation law cannot be proved. It can be verified, or disproved, by experiments. An experiment whose result is in
conformity with the law verifies or substantiates the law; it does not prove the law. On the other
hand, a single experiment whose result goes against the law is enough to disprove it.
It would be wrong to ask somebody to prove the law of conservation of energy. This law is an outcome of our experience over several centuries,
and it has been found to be valid in all
experiments, in mechanics, thermodynamics, electromagnetism, optics, atomic and nuclear
physics, or any other area.
Some students feel that they can prove the conservation of mechanical energy from a body
falling under gravity, by adding the kinetic and potential energies at a point and showing that it
turns out to be constant. As pointed out above, this is only a verification of the law, not its proof.
