In the early 20th particularly evident contradiction between classical wave theory of light, and the results of experiments.In particular, this concerned the photoelectric effect, which consists in the fact that the substance under the influence of electromagnetic radiation - in particular, the world - is capable of emitting electrons.This was pointed out by Einstein, as well as the ability of a substance to be in thermodynamic equilibrium with the radiation.

great importance in this case takes on the idea of ​​the quantization of the electromagnetic radiation (ie, making it only a certain value, indivisible portions - quantum) - as opposed to the wave theory, it is assumed that the energy of the el
ectromagnetic radiation can be any.

Background experience Bothe

idea of ​​the quantum nature of the electromagnetic radiation in general, and in particular the light was not immediately accepted by all physicists.Some of them are explained in the quantization of energy absorption and light emission properties of substances that absorb or emit light.This could be explained by a model of the atom with discrete energy levels - such a model developed by A. Zomerfeld, Niels Bohr.

The turning point was an experiment with X-rays, carried out in 1923 by the American scientist A. Compton.In this experiment, it was found the scattering of photons by free electrons, called Compton effect.At that time it was believed that the electron has no internal structure, therefore, it has energy levels can not be.Thus, the Compton effect proved the quantum nature of light.

experience Bothe

In 1925, the following experiment was performed, proving the quantum nature of light, to be exact - when the quantization of absorption.I put this experience German physicist Walter Bothe.

beam of X-radiation of low intensity working on a thin plate foil.This gives rise to the phenomenon of X-ray fluorescence, ie,foil itself emits a weak X-rays.These rays were recorded by two gas-discharge counters, which have been placed on either side of the plate.With a special mechanism meter readings were recorded on the tape.

From the standpoint of the wave theory of light energy emitted by the foil, should be distributed evenly in all directions, including in those where there were counters.The marks on the tape when it would appear simultaneously - one exactly opposite the other, but that did not happen: a chaotic arrangement marks speak of the emergence of the particles that were flying in one or the other direction of the foil.

Thus, the experience Bothe proved the quantum nature of electromagnetic radiation.Later electromagnetic quanta were called photons.