# Classical Explanation of Photoelectric Effect

1. Jul 4, 2012

### wilsonge

http://singlephoton.wikidot.com/single-photon-detection-experiment

I was browsing the web earlier, and noticed that the page above said that recently there was a semi-classical (wave) explanation of the photoelectric effect (End of 2nd-3rd Line). I was wondering how this was, as I can't seem to find any reference to it anywhere and was always taught this wasn't possible.

I thought I'd post here because I'm not sure whether this is genuine or whether this was one of these examples of never trusting a wiki site!!

Thanks in Advance :)

2. Jul 4, 2012

### mathman

I don't know what he is referring to. One glaring error: Einstein's work on the photoelectric effect was published in 1905, and that was his Nobel Prize paper.

3. Jul 5, 2012

### vanhees71

That's true. Ironically, this Nobel-prize winning paper is the only of Einstein's famous 1905 papers which is outdated today completely. The Nobel Commitee simply hasn't have the guts to give the prize to his really lasting achievements, i.e., general relativity or the statistical understanding of Brownian motion. The former is the fundamental (classical) theory of gravitation and has lead to a complete revision of our understanding of the fabric of spacetime and the latter has led to the proof of the existence of atoms and molecules as building blocks of matter and has been the breakthrough for kinetic theory proposed by Boltzmann and others, which is still today one of the most important subjects in physics (of course in its quantum many-body theoretical version). Contrary to that the old quantum theory by Planck, Einstein, and the young Bohr is obsolete with the discovery of modern quantum theory by Heisenberg, Born, Schrödinger, and Dirac in the mid 1920ies.

In fact you don't need QED to explain the photoelectric effect at all. The standard derivation is given in the lecture on quantum mechanics for electrons that are quasi-freely moving in the effective potential of the solid and irradiated with a classical electromagnetic wave, using time-dependent first-order perturbation theory. No quantization of the electromagnetic field is necessary to get Einstein's famous formula for the mean electron energy

$$E_{\text{el}}=\hbar \omega -E_{\text{binding}}.$$

Here $\omega$ is the frequency of the incoming classical em. wave and $E_{\text{binding}}$ is the binding energy of the electron to the solid.