Electromagnetic waves

Evolution of Quantum Physics The nature of light (radiation)

Evolution of Quantum Physics The nature of light (radiation)

                                Evolution of Quantum Physics The nature of light (radiation) has been a matter of long debate and a great confusion in the history of Physics. Rene Descartes, the father of the Cartesian geometry, first gave the corpuscular (particle) nature of light and the great Newton strongly supported him. Newton followed the corpuscular nature of light to explain the then known optical phenomena in his book ‘Optiks‘. C. Huygens, a contemporary to Newton, gave the wave theory of light and used the theory of secondary wavelets to explain the optical phenomena. Initially, both the theories were successful and it created a great confusion among the scientists whether Newton was correct or Huygens.

                                 After some years, Young performed the famous double slit experiment and the new optical
phenomena ‘Interference’. It put a challenge before both the theories of light to explain the interference of light. Newton’s corpuscular theory was failed to explain while Huygens’s wave theory was successful. After some time diffraction and polarization of light was also discovered and again corpuscular theory failed to explain these phenomena while Huygens’s wavelets theory was successful. Therefore, it was totally accepted that the light has the wave nature, not the particle nature. J.C. Maxwell theoretically proved that light is nothing but an electromagnetic wave and he was experimentally supported by Hertz. So, a lot of supports for the wave nature of light!

Evolution of Quantum Physics The nature of light (radiation)

                                         Classical wave theory of light was based on the principle that light is an electromagnetic
wave and the energy is distributed uniformly throughout the wave. This wave theory of light (radiation) was unable to explain some phenomena in physics e.g., Black body radiation spectrum, Photo-electric effect, Characteristic X-rays, stability of atom, specific heat of solids, Compton effect etc. These phenomena could only be satisfactorily explained using particle (Quantum) nature of light. For the first time, Max. Planck quantized the radiation emitted by black body and successfully explained the behavior of black body radiation which was unexplained using classical wave nature
of radiation (Wien’s law, Rayleigh-Jean’s law).

                                           Planck proposed that the radiation emitted is not continuous but it contains the tiny packets
of energy called ‘quanta’ and its energy is an integral multiple of hν where h is Planck’s constant and ν is the frequency of the radiation. Einstein followed the idea of quantization of radiation and successfully explained the photo-electric effect. Very soon, Planck’s quantization theory was popular among the scientists and used to explain all the unexplained phenomena of classical physics. Thus light has dual nature, sometimes behaves like a wave and sometimes, like a particle.

Evolution of Quantum Physics The nature of light (radiation)

                                        This quantum theory was only based on quantization of radiation, called as ‘old quantum
theory’. DE Broglie, in his PhD thesis, proposed that if wave (light) has particle (quantum) nature, on the basis of natural symmetry, a particle must have the wave associated with it. Very soon, it was  experimentally confirmed by Davisson and Germer that the electron shows the diffraction pattern and therefore has the wave associated with it. A year later, G. P. Thomson also performed an  experiment for high energy electrons and found in agreement with DE Broglie theory. Heisenberg and Schroedinger extended the wave nature of matter and described the particle as superposition of a lot many waves, a wave packet or wave group.

Dr. Deobrat Singh



Introduction to Quantum Mechanics by Pearson Education

Leave a Comment

Your email address will not be published. Required fields are marked *