Planck’s constant


The Planck constant is one of the fundamental constants of physics proposed by Max Planck in 1900 to explain the radiation of a black body . The radiated energy cannot take any kind of values ​​but only multiple integer values ​​of a quantum of energy. Planck’s constant links the value of energy to the frequency of radiation: E = hf . Planck’s work marked the beginning of quantum physics: light (and all forms of radiation) are emitted, transmitted or absorbed by discrete amounts of energy, the “quanta” of energy.


What is Planck’s constant?

It is a constant in quantum physics that allows us to determine the amount of energy corresponding to a quantum when it is used to multiply the frequency of radiation. It owes its name to the German physicist Max Planck, born in 1858.

  • History of Planck’s constant
  • What is Planck’s constant for?
  • Value
  • Planck’s constant formula
  • Importance

History of Planck’s constant

It could be said that Max Planck discovered the constant that bears his surname in the year 1900 in a forced way, since at this time, it was believed that the energy exchanges between matter and radiation were carried out continuously, while the experiments they proved otherwise.


On the afternoon of October 7, 1900, Max Planck and his colleague Heinrich Rubens discussed the latter’s measurements of the radiation of a black body (a black body perfectly absorbs all electromagnetic radiation), one of the most serious problems. thorny of the time. That same night, Planck empirically finds the law that describes the behavior of a black body, observed by Rubens.

Two weeks later, Planck and Rubens present their work at the University of Berlin. Then, on December 14 of that year, at the German Physics Society , Planck exposes the hypothesis that led him to this law: the quantification of energy. There he explains that the radiation emitted by a black body behaves as if it were made up of “packets” of energies whose value would be ε = hν, where ve is the frequency of the radiation and h is the constant known today as the constant of Planck.

This is how Planck solves the problem of the black body, raised by the physicist Gustave Kirchhoff in 1859 , who had studied the behavior of bodies in thermal equilibrium with the radiation that surrounds them.

Finally, it should be noted that in 1918, the German physicist received a Nobel Prize for his decisive discoveries that paved the way for quantum mechanics. Indeed, the Planck constant that associates the energy of a particle with its wavelength constitutes the fundamental magnitude of quantum mechanics.

What is Planck’s constant for?

Planck’s constant is used to describe the quantization phenomena that occur with particles and of which, certain physical properties take only multiple values ​​of fixed values ​​instead of a continuous set of possible values. For example, the energy of a particle is associated with its frequency by:

These quantization conditions are found throughout quantum mechanics.


Physicist Max Planck made a great contribution to quantum theory by discovering the value of a constant that would bear his name and which would express the minimum threshold of energy that can be measured in a particle.

The value of this constant is: h = 6.63. 10  -34  joules per second .

Planck’s constant formula

The formula developed by Max Planck is: E = hf , in which:

  • E = energy of the frequency;
  • h = Planck’s constant;
  • f = frequency of the wave.

Later, the physicist gives the name “quantum” to these quantities.


Planck’s constant introduces discontinuity in the description of elementary phenomena, which is the basis of quantum physics .

Thus, the importance of Planck’s discovery does not lie in a formal operation or in his mathematical ability. In reality, the significance of his proposal resides above all in the revolutionary interpretation of the physical meaning of the constant h . From the beginning, Planck attributed to the constant the name of “elemental quantum of action” because it has the dimensions of an action (energy multiplied by a time) since it only intervenes by multiple integers. Thus, Planck introduced the idea of ​​a granular composition when all physicists thought that continuity reigned.

To conclude, it can be seen that thanks to Planck’s formula the energy of radiation can be measured , not only in one unit of energy, but also in units of length and frequency . Also, using the black body law, you can determine the temperature of an object whose emission is centered at a certain frequency.

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