Talk:Photoelectric effect

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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.
Planck thought of light as a wave - and only as a wave. His idea was that matter emits and absorbs energy in quanta, but he didn't say anything about light-quanta. That's due to Einstein. As Planck credited Einstein for this achievement later on - so should you. Lenard's critique of Einstein - and the subsequently founding of the Deutsche Physik can't be taken serious: he didn't like Einstein's interpretations. Lenard made great contributions to the experiments of the photoelectric effect, but he didn't came forward with an adequate theoretical Überbau. All the proponents of the Deutsche Physik were vicious anti-quantum-mechanics. --BRichtigen 16:37, 25 October 2008 (EDT)
Planck may have been generous with credit. A lot of older scientists give excess credit to younger scientists. Einstein is peculiar in that he was well known for being very jealous about crediting anyone but himself. I don't know how you can say that Planck's idea was that matter emits energy in quanta, but not light-quanta. What happens when matter emits light? Planck and Lenard did get Nobel Prizes for their work. I don't know how you can act as if they did not understand what they were doing. RSchlafly 22:30, 25 October 2008 (EDT)
  1. Max Planck is often described as a reluctant revolutionary. His idea: matter emits energy in a certain quantum - you get a wave packet of a certain frequency. He didn't think of the emitted quantum as a photon,a corpuscle or particle. This was Einstein's idea. If this distinction is to subtle for you, well, remember that you are standing on the shoulders of giants, and while you may see more then them, you may miss some of the stones they stumbled upon once. And it was a great step, a ridiculous one to take, to think of light as particles: the wave-nature of light was well established, as Max Planck said, any other model would throw the theory of light back for decades, or even centuries...
  2. Philip Lenard was a great experimentator. And he received his Nobel prize for this work. He examined a phenomenon in great depths which couldn't be explained by the current theories . That these experiments can be performed nowadays in any well-equipped high school, doesn't mean that it was easy to perform them over a century ago.
  3. Philip Lenard didn't understand what he was doing. Michelson and Morley didn't understand what they were doing. Arno Penzias und Robert Woodrow Wilson didn't understand what they were doing. All of those had no - or the wrong - idea of the theories which lead to the observations by which they were puzzled. That's one point why there observations are cornerstones of the history of science.
  4. Einstein is peculiar in that he was well known for being very jealous about crediting anyone but himself. So was Gauss. And Lenard was a rabid anti-semite. All accounts agree - on the other hand - that Max Planck was one of the nicest guys you could ever meet - the Nazi propaganda called him a white Jew. All of them made valuable contributions to science. And one of Einstein's contributions was to explain the photoelectric effect by introducing light-quanta - an explanation, Lenard hadn't thought of and Planck was surprised by.

--BRichtigen 07:43, 26 October 2008 (EDT)

So you are saying that Planck's idea was that light is emitted in quantized wave packets of energy at a particular frequency, and Einstein's idea was that light is emitted as a particle. Einstein was correct while Planck was wrong or did not understand what he did or reluctant to take the quantum leap or otherwise somehow underdeserving of credit for quantizing light. Is that right? RSchlafly 11:36, 26 October 2008 (EDT)
I don't know whether my points were so garbled - or only your renarration of them is. Einstein's idea is that light can be regarded (at least sometimes) as existing from particles. Planck is clearly undeserving of credit for quantizing light - and stated so himself, several times. He gave full credit to Einstein, even under difficult circumstances, i.e., living in Nazi-Germany.
One could say that while Planck gave the energy of a quantum, Einstein gave its impulse. --BRichtigen 11:52, 26 October 2008 (EDT)
So are you saying that Planck said that light energy was quantized, and Einstein said that the light itself is quantized? What exactly is the difference? I don't get it. And where did Planck every say that he was undeserving of credit for quantizing light? RSchlafly 13:02, 26 October 2008 (EDT)
Here is Planck's Wahlvorschlag for Einstein from June 12th, 1913, i.e., his proposal to elect Albert Einstein into the Preußische Akademie der Wissenschaften - in this time one of the leading bodies of science. It's full of praise for Einstein, especially regarding the Theory of Relativity, and you'll find the lines I quoted above: "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)--BRichtigen 15:41, 26 October 2008 (EDT)
So Planck praised Einstein. Maybe Einstein deserved being elected to that group. I am not disputing that. Maybe Einstein said something about light quanta that Planck did not fully agree with. Planck does not say who deserves credit for quantizing light. Even if he did, the more significant fact is that Planck published five years earlier. RSchlafly 18:14, 26 October 2008 (EDT)
And Newton published 200 years earlier about light existing from corpuscles. But neither Planck nor Newton published on the photoelectric effect, using light-quanta. You may not like it, but Planck, Born, the Nobel committee, gave Einstein credit for his explanation - Lenard, of course, did not, not so much because of a priority dispute but as he didn't accept the jüdische Physik ... --BRichtigen 18:32, 26 October 2008 (EDT)
And here is a nice - albeit secondary - quote from the Encyclopaedia Britannica: These oscillators of frequency ν are incapable of absorbing or emitting electromagnetic radiation except in energy chunks of size hν. To explain quantized absorption and emission of radiation, it seemed sufficient to quantize only the energy levels of mechanical systems. Planck did not mean to say that electromagnetic radiation itself is quantized, or as Einstein later put it, “The sale of beer in pint bottles does not imply that beer exists only in indivisible pint portions.” The idea that electromagnetic radiation itself is quantized was proposed by Einstein in 1905, as described in the subsequent section. As usual, they express the thoughts so much clearer then I can do it... --BRichtigen 18:50, 26 October 2008 (EDT)
I am happy to give them all the same credit that the Nobel committee gave them, but the Nobel committee did not credit Einstein with quantizing light. RSchlafly 21:38, 26 October 2008 (EDT)
Hopefully my edits cleared up all the issues over the Nobel prizes. The quotes are directly from the webpage of the Nobel Foundation. Ed: Forgot to sign ArnoldFriend 18:11, 27 October 2008 (EDT)
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