The German physicist Max Karl Ernst Ludwig Planck (1858-1947) began to study blackbody radiation in 1897, seeking theoretical solutions to an equation proposed by Wilheim Wien, also a German physicist.
Soon, large discrepancies with the experimental results for low frequencies were detected in the Wien formula. Planck then sought to find out what these results were and looked for an expression that would fit.
The spectrum of blackbody radiation was the most important of these studies, as the radiation emitted by the blackbody is scattered by a prism of non-absorbing material and directed to a detector that measures the intensity of each frequency of radiation. Such experimental setup allows obtaining graphs of the radiation power emitted by the black body that reaches the detector by area and frequency (W/m².Hz), for each temperature as a function of frequency.
Although these graphs have well-defined characteristics, classical physics could not explain them, and it was not possible to obtain a mathematical equation based on the principles of classical physics, known at the time.
So Planck, “in an act of desperation”, decided to reverse the theoretical process, starting from the graphs to arrive at the equation. Not satisfied, he began to look for a theoretical justification to support it. He found between the concepts of entropy and probability of thermodynamics a function where all terms had a physical meaning. Thus, Planck’s constant was born.
h = 6.63 .10 -34 J.s h = Planck’s constant
Energy (action) only exists in nature in discrete values in action quanta, that is, this process gives nature a discontinuous character, unacceptable for classical physics.
Abstract: Planck discovered that action, a magnitude that nature always uses in the smallest possible amount, cannot be infinitely small, because it has a limit value; although it is very small, this value is imposed by nature itself, h = 6.63 .10 -34 Js