Talk:Photoelectric effect

Tesla / radiant energy
Tesla specifies that the exposed plate is insulated. It seems that the insulation should prevent light from hitting the metal plate directly. Or if transparent, the insulator should prevent electrons from being ejected. If so, how is this consistent with the photo-electric effect?

I have always been under the impression that static electricity actually drove Tesla's invention (triboelectrification between dust and the insulator). Alternatively, the device may be driven by photon induced ionization of the air. In either case, the capacitor may then be inductively charged.

Can anybody resolve this objection, or link to a careful discussion of Tesla's "radiant energy" device and the photoelectric effect?


 * (William M. Connolley 19:30, 31 Aug 2004 (UTC)) I can't answer your point, but I have deleted the "Radiant energy" section, which appears to be dubious at best. If Tesla described/explained photoelectricity in 1901, as the section claims, he has great priority: Lenard's obs were not until 1902 . So I don't believe this claim. At best, Tesla obtained a patent on a device using PE. He did not describe PE (important points being dep n freq not intensity) - or if he did, there is no evidence presented for this.

Connolley, read the damn patents! Specifically ...


 * US685957 - Apparatus for the Utilization of Radiant Energy
 * US685958 - Method of Utilizing of Radiant Energy

The tube (marked as S) is cited in the patents as a Lenard tube or Roentgen tube. As to describing the PE, a basic description is in the patent ... if you read it!


 * (William M. Connolley 18:08, 20 Apr 2005 (UTC)) Tesla isn't in the std history of the photoelectirc effect. If you really think he belongs in the history, then he needs to be put in explicitly, not sneaked in via a "patents" section. And to do that, you need a proper source, because the patents don't seem explicit enough to me. Note that you have ignored my points above, viz: He did not describe PE (important points being dep n freq not intensity) - or if he did, there is no evidence presented for this.. I don't see anything in the patents addressing this - do you? I hope someone mopre competent will comment.


 * It's IRRELEVANT if Tesla isn't in the std history of the photoelectirc effect. He has been left out of a great many things in which he should be credited for. But the main source of information is from his patents ... so this probably would be better place for him. It's not "sneaked in", just a statement of facts.
 * The patents are pretty explicit, if you read them carefully (not just brush over them). Remember ... this (1901) is before much of the terminology is coin that we use today. The evidence is the 2 patents! NOTICE what the examiner wrote on the patent [it's in terms similar of which Thomson used].
 * As to describing the PE (I think you are menting depletion and frequency [dep n freq )... this is in both ... let's take US685957, in the 1st page of the description on lines 11-34 he mentions "vibrations" of "small wavelengths" ... he then goes on to note that HIS observations call for a new theory that is being advance in the patent about "minute particles" "electricified" [eg. electrons] and being thrown off.
 * If you can't comprehend this, you are not ignorant ... but an idiot


 * (William M. Connolley 19:39, 20 Apr 2005 (UTC)) It is highly relevant that T is not in the std history, since wiki is a summary of the general state of knowledge, not of your personal research. The patents do not seem at all explicit to me, and I note that you have not actually quoted the text from them: please do so if you think it is relevant. Your third point remains off the point. For your fourth point, you are reminded of the "no personal attacks" rule.


 * Wikipedia is a secondary source (smetimes a tertiary source) ... not just a summary of general knowledge ... eg., material that has generalization, analysis, synthesis, interpretation, or evaluation. This isn't my "primary" research ... but public knowledge from primary sources.
 * Patents are explicit and I have cited lines in the patent! (eg., 1st page of the description on lines 11-34)
 * I applogize for any "attack" ... but there are only so many conclusions to come to when facts are stated and then are ignored.

User:204.56.7.1 has put nonsense about Tesla discovering superconductivity on List of Tesla patents and Superconductivity. He seems impervious to facts. pstudier 20:45, 2005 Apr 20 (UTC)


 * He added stuff to solar cell too. - Omegatron 20:51, Apr 20, 2005 (UTC)

Ok, I didn't really have an opinion before (except skepticism of hero worship), but I've been reading a lot and this does look like the photoelectric effect to me. Yes, it's original research, but I'm finding some cool things to include in various articles while I do it. :-)

"It is well known that certain radiations — such as those of ultra-violet light, cathodic, Roentgen rays [X-rays], or the like — possess the property of charging and discharging conductors of electricity, the discharge being particularly noticeable when the conductor upon which the rays impinge is negatively electrified." As long as the charging is positive and the discharging is of a negative object (as he seems to say in the second phrase), this is pretty much a statement of the photoelectric effect. However, his explanation for it ("that sources of such radiant energy throw off with great velocity minute particles of matter which are strongly electrified, and therefore capable of charging an electrical conductor") is wrong. He also says it is "well-known", though, so he isn't claiming to have discovered it; just demonstrating a way of capturing the energy.

A metal like aluminium has a work function of 4 eV. This means that to eject electrons from the surface through the photoelectric effect it needs to be hit by EM with a frequency above about 1 petahertz: math This is equivalent to a wavelength less than 310 nanometers math. This is in the range considered "near UV". So, through the photoelectric effect, UV and X-rays hitting a piece of metal will knock off electrons and give it a positive charge, as he said ("As the rays or supposed streams of matter generally convey a positive charge to the first condenser-terminal"). (But not visible light, so this has nothing to do with solar cells.)

As the charge gets bigger, though, the work function changes, so this only goes on until the charge is high enough that the electrons can't leave anymore. By connecting a large-value capacitor to the plate and the other side connected to a large charge reservoir (the earth), you can knock more electrons out of the plate than normal, because the capacitor "condenses" charge into a smaller space than the charge would normally fill by attracting it to opposite charges on the other plate. That's why they used to call them "condensors". So far, so good.

(Yes he does say something about the "receiver" being an "insulated plate or conducting-body", which made me think "coated in plastic" at first glance, but he also says "the surface should be clean and preferably highly polished or amalgamated", so I think he just means supported in a way that it is insulated from other objects, like you would say an insulated sphere of metal has a charge on it.)


 * Here is a sort of similar experiment: (fig. 3)

The one thing I'm not completely sure of yet is whether the photoelectric effect would create a net charge on a piece of metal in air.


 * This seems to indicate that yes, you can emit the electrons into the air (only if the metal is charged negatively in the first place?)


 * This says "Absorption in air by X-rays is minimal and the arriving X-rays have their full energy. Electrons, on the other hand, lose energy and are scattered by air". Since their testing depends on catching those electrons, they do their tests in a vacuum.  In this case, though, the scattering of the electrons doesn't matter.


 * Tesla's (clever) metal foil switchy-thing discharger is specifically "inclosed in a receptacle, from which the air may be exhausted", which implies to me that the rest of the device is not. Hmmm...

But where do the electrons go? They just attach to the air and ionize it? Wouldn't they then drift back and stick to the metal and neutralize? Maybe it takes a while for them to drift back and neutralize, and you can discharge it into the earth before that happens (and then they will have to drift down to the earth to neutralize instead). Does a charged sphere eventually discharge by contact with the air? I'm used to thinking of circuits; not isolated charged objects. "The typical atmospheric molecule has an energy of about 0.03 eV." Aha! The electrons are tiny and also have >100 times as much energy. So maybe that is what happens. This paragraph should be considered much more speculative than the others, though. :-) I'm really out of my element with the air charge stuff. - Omegatron 02:37, May 21, 2005 (UTC)

Moon dust
Are we sure that the moon dust gains its charge from the photoelectric effect and not from the charged particles streaming from the Sun? Enochlau 10:29, 21 Jun 2005 (UTC)


 * Did you check the references? Read this right after the balloon hair picture. - Omegatron 13:37, Jun 21, 2005 (UTC)
 * Hmm interesting, thanks.Enochlau 23:32, 21 Jun 2005 (UTC)

Einstein was correct
The end of the second paragraph states that Einstein was correct, but it does not say what he was correct about. — Preceding unsigned comment added by 66.92.187.113 (talk) 22:22:50, March 21, 2007 (UTC)


 * The last revision before the previous comment does have that problem in the third paragraph (first paragraph in the "Introduction" section). Brian Jason Drake 08:14, 16 October 2009 (UTC)

{this part by the way has nothing to do with the other articles}. even though I use wikipedia a lot, some info in here i found out was fake. you could edit it like I am just doing, so people could make things up. — Preceding unsigned comment added by 2601:8C3:4100:7350:E1C6:D18:5EE7:7DB2 (talk) 03:34, 21 March 2018 (UTC)

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Just like an Oscar
Article currently says;


 * Einstein was awarded the Nobel Prize in 1921 

The following is in my Nobel Prize book, and some official-looking Nobel site; Einstein was awarded the Nobel Prize in 1922 for 1921. The award was “reserved” in 1921. MBG02 (talk) 22:19, 6 September 2018 (UTC)
 * --Thrasymedes (talk) 19:41, 2 February 2020 (UTC)

The lead needs work
I came to this article from a Google search looking for a place to start background research on the photoelectric effect but the article is a mess, especially the lead. As flagged already, the lead is way too long. Beyond this, Heinrich Hertz is not mentioned but should be. The entire lead lacks a single primary source. Photoemission-specific review articles are absent as well. Unfortunately, I don't have time at present to conduct an overhaul, but would encourage others to take a look and start making corrections if possible. I might be able to get around to doing some of this myself sometime in the next year or so. A few suggested references to add in might be H. Hertz, Ann. Physik 31, 983 (1887) [referenced in places other than the lead as Ref. 22], the review article by H. P. Bartel Ch. Kleint: Prog. Surf. Sci. 49, 107 (1995), and the textbook Photoelectron Spectroscopy by Stefan Hufner. Csmallw (talk) 18:18, 19 July 2019 (UTC)

Millikan's experiment
The article says:
 * In 1914, Millikan's experiment supported Einstein's model of the photoelectric effect.

But isn't Millikan's experiment (which redirects to the oil drop one, published 1913) a different one to the photoelectric effect experiment (published 1916)? So the wikilink and year might be misleading here? (However, he did start his photoemission experiments several years before he published the 1916 paper, according to Abraham Pais's 1979 review.) Or is there a connection to the oil drop experiment as well? Either way, I think it could be made more clear. David R. Lloyd published a review in 2015 of Millikan's photoemission work which cites the 1916 paper and not the 1913 paper. --Thrasymedes (talk) 19:33, 2 February 2020 (UTC)


 * I agree, the link shouldn’t be there, and the date should reference 1916 rather than 1914. It may need a qualification to distinguish it from the oil-drop experiment, especially since both were referenced in the Nobel Prize he received as described later in that paragraph. Perhaps the following: "In 1916, Robert Millikan published experimental results that supported Einstein's model of the photoelectric effect (not to be confused with Millikan’s famous oil drop experiment)." — Andy Anderson 21:43, 2 February 2020 (UTC)
 * That sounds good to me as a summary. Having read the article more thoroughly, I have found the likely source of the 1914 date, and the situation is a bit more complicated than I first thought. In the article, we have another reference to Robert Millikan's experiment, "However, the manner of the increase was not experimentally determined until 1914 when Robert Andrews Millikan showed that Einstein's prediction was correct." This cites a different paper to the 1916 one and would explain the 1914 date:
 * This is a much shorter paper than the famous 1916 one (which is marked 'Featured in Physics' by the APS), and it has 80 citations compared to 382 (Google Scholar). It has a very similar title and seems to be along the same lines as the 1916 one. It confirms Einstein's predictions, but does not provide explicit support like the 1916 one. The 1916 article seems to be much more detailed and finishes with a Summary in strong support of Einstein's equation (p. 388): "Einstein's photoelectric equation has been subjected to very searching tests and it appears in every case to predict exactly the observed results." A 2013 paper by Allan Franklin, "Millikan’s measurement of Planck’s constant", discusses the history in more detail, including the 1914 paper. In the Background section of his paper, shortly after discussing the 1914 one, it says "... This was the situation when Millikan began his 1916 work on the photoelectric effect. There were considerable differences in both the experimental results and in the interpretation and evaluation of those results." Based on this section, I get the impression that the 1914 paper was a stepping stone among other similar papers by different authors, and that the 1916 paper was the crucial one that convinced the physics community that Einstein's equation (but not necessarily theory?) was correct. As the APS article says, "Robert A. Millikan’s 1916 paper on the measurement of Planck’s constant was dramatic in its time." So perhaps we need to explain both papers and the progression between them? Or perhaps we need to talk about more than these two papers? Or, if we are being brief, should we only talk about the 1916 paper since this seems to be the most important one?
 * This 1914 paper, one page long, is footnoted with “Abstract of a paper presented at the Washington meeting of the Physical Society, April 24, 1914”, as is the previous article. So these are conference proceedings, a way to effectively establish precedence of results that are first presented in public and may not have all of the experimental justifications provided. They are therefore probably less subject to peer review (?) than his 1916 paper. Who knows, the two-year delay may be due to the reviewers putting Millikan through the ringer :-). Because of this, I still think 1916 would be the appropriate one to reference. — Andy Anderson 22:42, 6 February 2020 (UTC)
 * I've found that Robert Millikan published another paper on the topic earlier in 1916:
 * This starts off saying, "[Einstein's photoelectric equation] cannot in my judgment be looked upon at present as resting upon any sort of a satisfactory theoretical foundation." It goes on to say, however, "I have in recent years been subjecting this equation to some searching experimental tests from a variety of viewpoints and have been led to the conclusion that, whatever its origin, it actually represents very accurately the behavior, ..."
 * I looked for a recent study that touches on the history of the photoelectric effect, and this 2010 paper by Mansoor Niaz, Stephen Klassen, Barbara McMillan and Don Metzhas has some interesting remarks that caution on the distinction between the acceptance of Einstein's equation and Einstein's theory:
 * In a recent study, Holton (1999) has asked a very pertinent question: “So Millikan's (1916b) paper is not at all, as we might now naturally consider it to be, an experimental proof of the quantum theory of light” (p. 232). This statement has important implications. The 1916 publication was considered by its own author as an experimental test of Einstein's photoelectric equation and in no way a confirmation of the underlying hypothesis of lightquanta (Millikan, 1916b). On the contrary, most textbooks and physicists at present would consider Millikan's (1916b) experimental data as evidence for Einstein's quantum theory (hypothesis of lightquanta). ... Among the most prominent physicists not to accept Einstein's theory for some time were Max Planck and Robert Millikan. Millikan, although he was able to demonstrate Einstein's equation experimentally with a high degree of precision, did not accept the quantum hypothesis until much later.
 * Allan Franklin's paper seems to corroborate this, saying, "[Robert Millikan] is often mistakenly given credit for providing significant evidence in support of Einstein’s photon theory of light."
 * Also, as Csmallw alluded to above, I think the article could do with some reorganization. Should the whole paragraph starting "In 1900, while studying..." be merged into the next section (20th century as opposed to 19th) since those years are part of the 20th century? We also seem to have repetition of discussion of Albert Einstein and Robert Millikan's work. Would this be better combined? --Thrasymedes (talk) 22:18, 6 February 2020 (UTC)
 * Allan Franklin's paper seems to corroborate this, saying, "[Robert Millikan] is often mistakenly given credit for providing significant evidence in support of Einstein’s photon theory of light."
 * Also, as Csmallw alluded to above, I think the article could do with some reorganization. Should the whole paragraph starting "In 1900, while studying..." be merged into the next section (20th century as opposed to 19th) since those years are part of the 20th century? We also seem to have repetition of discussion of Albert Einstein and Robert Millikan's work. Would this be better combined? --Thrasymedes (talk) 22:18, 6 February 2020 (UTC)

Planck rejected the concept of photons (light quanta) as late as 1913
In the "Theoretical explanation" section the article states "In 1905, Einstein proposed a theory of the photoelectric effect using a concept first put forward by Max Planck that light consists of tiny packets of energy known as photons or light quanta."

In 1900 Planck derived his well known black body radiation formula by requiring resonators (oscillating charges) comprising the wall of the black body cavity to take on only integral multiples of energy hf (E_resonator = nhf, where n is an integer). A number of reputable physics histories point out that he continued to believe electromagnetic radiation emitted and absorbed by the resonators was continuous and wavelike (not quantized). Planck did not comfortably relinquish his devotion to the well established classical (Maxwell) description of continuous radiation even after Einstein's 1905 paper proposed light quanta as a fitting explanation for the photoelectric effect.

As late as 1913, in his recommendation of Einstein to the Prussian Academy of Science, Planck stated: “That sometimes, as for instance in his hypothesis on light quanta, he may have gone overboard in his speculations should not be held against him.” 74.119.23.6 (talk) 00:11, 18 December 2022 (UTC)

Einstein's photoelectric effect paper did not agree with frequency dependence experiments.
I have edited the 20th century section to remove the idea that Lenard or anyone else studied the frequency dependence of the photoelectric effect before 1905. There were no such experiments. He predicted the effect. Took 10 years to verify.

Added a ref to a historical analysis: Lenard made no attempt in this study or in subsequent studies to correlate light frequency with electron velocity. Johnjbarton (talk) 03:51, 8 July 2023 (UTC)

Abundance of Photon-Matter Interaction with various processes
@Dougsim added a figure with a caption Caption does not describe the figure. I can't tell what the markings in the diagram mean, or the axes for that matter. How it is related to the article topic? Johnjbarton (talk) 14:37, 21 June 2024 (UTC)
 * Abundance of Photon-Matter Interaction with various processes


 * @Johnjbarton, this is, supposedly, showing at which photon energy for some element the favored process (by cross section) switches from PE to CS to PP. The figure illustrates that section pretty well, imo. Ponor (talk) 16:02, 21 June 2024 (UTC)
 * @Ponor Please add a reference and improve the caption. As it stands the figure is unintelligible. It plots atomic number vs Energy. Why? Energy of what? Theory? Experiment? Conditions? Johnjbarton (talk) 16:09, 21 June 2024 (UTC)
 * I tried to keep the new caption short, feel free to improve. The cross section values can be calculated online (here), the values for Z=20 seemed to be consistent with the plot. Ponor (talk) 16:54, 21 June 2024 (UTC)
 * @Ponor thanks, that's much better Johnjbarton (talk) 18:54, 21 June 2024 (UTC)