Blackbody Spectrum - Planck's Quantum Theory

This video discusses Max Planck's Quantum Theory of radiation. The complete derivation of Planck's law and Plank's formula for the blackbody spectrum is discussed and derived. The video begins with a discussion of the definition of thermal radiation and blackbody. Thermal radiation is basically electromagnetic radiation. The video goes on to explain the two types of blackbodies that could exist there and the nature of the blackbody spectrum. Irrespective of the material composition, all blackbodies exhibit a spectrum of universal character. Most blackbodies that are constructed in laboratories are the cavity type and the cavity radiation that escapes out through a hole in the cavity is blackbody radiation. The peculiar nature of the spectrum was investigated by several physicists during the late 19th century. The empirical results obtained by Stefan and Wiens are important and we know these as Stefan's law or Stefan-Boltzmann law and Wiens' displacement law respectively. The first significant theory on the blackbody is owing to Rayleigh and Jeans. The theory could explain the nature of the spectrum at low frequencies. But at high frequencies, Rayleigh and Jeans theory leads to what is called as Ultraviolet Catastrophe, which is explained in the video. Among the several physicists that were concerned about the ultraviolet catastrophe was Max Planck who proposed his "On the theory of the energy distribution law of the normal spectrum" on the 14th December 1900 which we now know as the Quantum Theory of radiation. Planck's genius lay in his understanding that energy is quantized and that the distribution of energy or discretization is uniform as well. A graphical approach to understanding Planck's probable thought process is provided.The video goes on to explain in detail Planck's approach to providing a solution to the blackbody spectrum that not only avoided the ultraviolet catastrophe but also ensured a perfect foundation for a new theory that changed the way we understand nature. The discussion on the derivation of Planck's law begins at the Rayleigh and Jeans result and moves on to provide the complete derivation leading to Planck's law. Then, the low frequency and high frequency test cases of the Planck's formula are discussed. The blackbody spectrum is discussed from both the wavelength and the frequency perspectives. Finally, the video concludes with a discussion on how Stefan's law and Wiens displacement law are special cases of Planck's law and how this could be used to calculate two of the fundamental constants in Physics namely the Boltzmann's constant and the Planck's constant.