Talk:Photoelectric effect

Timeline

While Philip Lenard made very important observations during his experiments with the photoelectric effect, his were the heuristic explanation. Albert Einstein came up with the theoretical framework, the quantum theory of light. He used the ideas of Max Planck - but Max Planck himself didn't recognize this work fully until the first Solvay conference: His first reaction to Einstein's explanation wasn't overwhelmingly friendly

"Es scheint mir, dass gegenüber der neuen Einsteinschen Korpuskulartheorie des Lichtes die größte Vorsicht geboten ist... Die Theorie des Lichtes würde nicht um Jahrzehnte, sondern um Jahrhunderte zurückgeworfen..."

(It seems to me that regarding Einstein's corpuscular theory of the light the greatest caution is to be advised... the theory of light could be thrown back not only for decades, but centuries...)

I changed the article according to these observations back to the previous version. --BRichtigen 08:16, 23 October 2008 (EDT)

It was Planck who said that light was quantized, with E = hf. It is Planck's constant, after all. And that was before Einstein's paper. I think that it is more accurate to call it Planck's quantum theory of light. RSchlafly 17:51, 23 October 2008 (EDT)

Well, Planck himself spoke of "Einsteins Korpuskulartheorie des Lichtes" - the Einsteinian corpuscular theory of light...

In 1900, Planck initiated the quantum physics (Quantenphysik) with his speech Zur Theorie des Gesetzes der Energieverteilung im Normalspektrum (About the Theory of a Law of the Distribution of Energy in the Normal spectrum). Here, he thought of the material as oscillators which could send out energy only in special quanta. This is thought as a property of the material, not of the electromagnetic waves which were produced. Especially, he didn't state that light was quantized - the opposite is true. Einstein was the first to undertake the step to think of the waves as quantized in 1905 (Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt - About an Heuristic Aspect Regarding the Generation and Transmutation of Light). And while Planck's view in 1900 was radical new, this was also radical new, but different. That's why Planck took quite a while to accept this new aspect.

Dear RSchlafly, I looked at your contributions to the articles regarding A. Einstein: you seem to be very critical toward Einstein's contributions to modern physics. But here, you should go with Max Planck and accept that it was Einstein's idea of a quantum theory of light - which gained him the Nobel prize rightly, I'd say.

Nowadays, it seems so natural for us to think of light as quantized that we often fail to see how difficult - and counter-intuitional - this idea was at the beginning of the 20th century: it had taken so long to think of light as waves after the bitter Newton/Huygens controversy...

--BRichtigen 08:07, 24 October 2008 (EDT)

I am all in favor of crediting Einstein for what he actually did, but it was Planck who postulated that light was quantized, and Lenard who explained the photoelectric effect. This is conventional wisdom -- Planck and Lenard got Nobel prizes. Eg, Planck is credited for this:

In a paper published in 1900, he announced his derivation of the relationship: this was based on the revolutionary idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant.[1]

I also don't believe the photoelectric effect was the reason Einstein got the Nobel prize. Einstein was already famous for relativity, and the committee felt pressure to give him a prize, but a prize for relativity would have been controversial for various reasons. RSchlafly 18:34, 24 October 2008 (EDT)

This conventional wisdom is superficial: Planck stated that light can only be emitted or absorbed in discrete quanta, Einstein stated that light itself existed from discrete quanta - a quantum leap from Planck's idea, if you allow for this brutal metaphor.

From the same source you used: By exact measurements he [i.e., Lenard] showed that the number of electrons projected is proportional to the energy carried by the incident light, whilst their speed, that is to say, their kinetic energy, is quite independent of this number and varies only with the wavelength and increases when this diminishes.

These facts conflicted with current theory and were not explained until 1905, when Einstein produced his quantitative law and developed the theory of quanta of light or photons, which was verified much later by Millikan.[2]

So, Lenard didn't give an explanation for this phenomenon, but examined it in great detail.

In 1905, Max Planck was still of the opinion that light is only to be seen as a continuous wave, in fact, even in 1913 he -together with Nernst, Rubens and Wartburg - stated in his Wahlantrag for the Preussische Akademie der Wissenschaften for Einstein: "Daß er in seinen Spekulationen gelegentlich auch einmal über das Ziel hinausgeschossen haben mag, wie z.B. in seiner Hypothese der Lichtquanten, wird man ihm nicht allzu sehr anrechnen dürfen. Denn ohne einmal ein Risiko zu wagen, läßt sich auch in der exaktesten Wissenschaft keine wirkliche Neuerung einführen." (He may have overshot the mark with his speculations sometimes, as regarding his hypothesis of the light quanta, but one can't hold this against him. Because without taking a risk, nothing really new can be introduced into the most exact of sciences)

Einstein was awarded the Nobel prize for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect. Surely, the Nobel committee could have chosen from quite a few reason to give it to him, but it used this one. --BRichtigen 23:11, 24 October 2008 (EDT)

I don't see why it matters if Planck said in 1913 that light is a wave. Light can be understood as waves or particles. Just tell me what Einstein did that was original. I do not want to give Einstein credit for what Planck and Lenard already did.