Heinz Heinzmann

Photoelectric Effect

Wave or Particle?

In 1905 Einstein explained the photoelectric effect with the assumption that the energy of the radiation field is quantized.

The experimental facts of the photoelectric effect:

If a metal plate gets irradiated by UV-light with a frequency ν above a certain limit ν0 , electrons are set free without any delay. The kinetic energy of these electrons depends only on the frequency ν of the radiation.

This is in blatant conflict with the wave model of the light, according to which the displacement of electrons should take place at any light frequency and their energy should have to be dependent on the intensity of the light. Furthermore, an enormous delay (under realistic conditions thousands of hours) until the displacement of the first electron would have to be expected.

As is well known Einstein’s solution was to assume an interaction between light and matter in form of an impact process of particles, i.e. of a light-quant with the energy hν and an electron bound with the energy A. Then from the energy balance the following relation results:

hν      =       A    +   mv2/2      (A … displacement work)

Let us first ask which concrete model assumptions lead to the contradiction to the wave model of the light.

The answer is straightforward: The contradiction follows from the simple assumption that the interaction between light and electrons takes place according to the paradigm of macroscopic, “mechanical” interactions – not different from e.g. water waves and pebbles. Would this be the case, then as a matter of fact it would have to be expected that the kinetic energy of the electrons depends on the intensity of the light. (Thus it is the origin of physics from mechanics, which leads to these contradictory model assumptions).

However we now show:

If both, light and electron are understood as waves then we obtain the same result already under the simplest model assumptions.

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