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Archive 1

Old discussions (2004)

I have changed the first sentence:

The photoelectric effect is the emission of electrons from a usually metallic surface upon exposure to, and absorption of, electromagnetic radiation, such as visible light or ultraviolet radiation.

to:

The photoelectric effect is the emission of electrons from matter upon the absorption of electromagnetic radiation, such as visible light or ultraviolet radiation.

Usually is meaningless. Photoelectrons produced from non metalic solids, liquids and gasses is of as much interest as the photoelectric effect from metals. Saying that the matter is exposed to and then absorbs light is redundant. The absorption of a light implies that it has been exposed to the light.

The point is whether we should define the photoelectric as "flow of electric current in a material when it is exposed to light" or a "emission of electrons from a material when it is exposed to light". I think the latter is preferable for the following reasons:

  • The historical argument. I think that the first demonstration of the photoelectric effect was the observation of discharges (due to emission of electrons) between electrodes induced by ultra-violet light by Heinrich Hertz.
  • A current will flow in a metal when exposed to ultra-violet light, but that is a secondary effect due to the holes left behind in the photoemission process. One can also knock electrons out of free atoms by photons, and in this case it does not make much sence to speak of current flowing.
  • Photoemission spectroscopy, the detection of electrons from a solid (or liquid) with respect to kinetic energy and emission angle, is an important technique in solid state physics.

What do you think?

I agree with the latter. A current is caused by energetic electrons, and is not always present in a demonstration of the effect. -Twinxor

As a reader of an encyclopedia, I would like to see reference to application of the scientific discoveries. Did this discovery brought us technologies that we used today or in the past? How did it change our life? Are solar power, digital cameras etc. based on this effect?

Please consider adding an "Applications" section to all entries that are related to science and technology.

My impression was that the current-flow effect was discovered first; if I am mistaken about that, and the first observations were simple discharges, then that might be a better starting place. I just wanted to make clear the distinction between Einstein and others' explanation of what causes the effect from the simple observation of the effect itself. I agree that mentioning applications would be good. Probably the earliest and best known was talking pictures: the soundtrack on a piece of movie film works by shining light through that portion film as it moves, stimulating an electrical current attached to sound amplifiers. --Lee Daniel Crocker I want to know why my question about Hertz as the discoverer of the photoelectric effect was not answered and erased instead.

That's not the best example. The first optical soundtrack system, Movietone, used a photocell, which is a light-dependent resistor and has nothing to do with the photoelectric effect, and I believe that modern analogue optical soundtracks still use photocells. I think this is because photocells are more linear than photodiodes. Digital optical soundtracks, such as the Dolby digital system, are a different matter: they probably use photodiodes, because linearity is not necessary in a digital system. -- Heron 10:34, 10 Jul 2004 (UTC)
Oops. I have just checked my facts, and found that my comment above was wrong. It seems that photocells and photodiodes both use the photoelectric effect. -- Heron 10:39, 10 Jul 2004 (UTC)

The emission of electrons is a more precise statement and should therefore replace "current flow." In fact, "current flow" brings to mind electrons (or charge) flowing within the material, but in the photoelectric effect the electrons are ejected and completely escape the material. --Carlos M.

"Emission of electrons" is clearly wrong, precisely because it is more accurate! Again, let me be clear: physicists (probably Hertz, but others might have noticed it earlier) observed some effect long before they knew that it was in fact the emission of electrons. It was later discovered what caused the effect, but the effect itself should be described as whatever the actual measurement or observation was that led us to figure it out; not what we currently understand as its cause--that's circular definition, and bad science. If what Hertz first measured was the discharge of a plate or a Leyden jar (as I now suspect), then define it that way. If what he first measured was a current flow (which I first assumed, perhaps erroneously), then say that. I'm not sure which it was, but I do know for sure that Hertz did not observe the emission of electrons. --[[User::Lee Daniel Crocker|LDC]]

I see no a priori reason why the definition should be based on what led scientists to discover the effect.
  1. Such an approach is clearly anthrocentric, which some might not mind.
  2. Such a definition would mean that many phenomena would no longer be consider manifestations of the photoelectric effect. For example, there is no current caused in the levitation of moon dust.
  3. Such a convention would require rather severe changes in other terms. Do we want to define electric current as "the thing that happens in a frog's leg when placed on a moist tin dish and prodded with a lead knight"?

Phantym 19:27, 22 May 2005 (UTC)

Counter Intuitive?

The dual nature of the photoelectric effect, wave or particle, made it very hard to accept. Does this count as Counter-intuitive?

Tabletop 10:56, 31 Mar 2005 (UTC)

I'm slightly confused. What dual nature of the photo-electric effect are you referring to? Do you mean the suggestion that (because of the photo-electric effect) light is a particle (which was previously thought of as a wave?) Or am I missing something completely? Pubuman 15:37, 10 August 2006 (UTC)

Replace 'wavelength' with 'frequency'?

not to split photons but...

Under explanation: "The photons of the light beam have a characteristic energy given by the wavelength of the light"

Actually, isn't it the frequency that defines the energy? The wavelength varies depending on the medium but the medium does not affect the energy of the photon.

~Peter —The preceding unsigned comment was added by 129.237.121.29 (talk) 19:05, 4 January 2007 (UTC).

Correct; the frequency is what determines the energy. I've changed it. Uberdude85 20:41, 11 March 2007 (UTC)

Replace image

Hello everyone I would like to know if the lead image of the article

be substituted by an animated pic

LegalEagle 05:58, 25 February 2007 (UTC)

Photocopier

From what I understand a photocopier makes use of a photo sensitive drum as an important part of its copying cycle. Am I correct in assuming that this drum exploits the photoelectric effect? If so i believe that the photocopier should be added to the list of applications as this effect is central to the photocopier's operation. Aamackie (talk) 02:31, 10 January 2008 (UTC) Sorry, just did a little research, it doesn't use the photoelectric effect. Aamackie (talk) 01:52, 17 January 2008 (UTC)

Removal of text

I removed the following piece of text.

Lee Hock Cheong's Photoelectric Effect using the Hexaton Atomic Model

As the proton is much larger than an electron, the probability to interact with a photon compared with an electron is therefore higher. When a nucleus absorbs a photon, the increase in energy will result in the displacement between the electron and the nucleus to be larger. This lets the orbital elecron escape from the magnetic and coulomb attraction of the nucleus with lesser kinetic energy than before. This is different from that presented by Albert Einstein, where he designated the electron as the vehicle for the absorption of photon as opposed to the proton forming the nucleus of the atom.

There are just 31 hits in total on Google, and this guy seems to be going against everything that is commonly accepted in the scientific circles. This sounds like one crackpot theory to me. (And we should check other pages to see if this guy's theory has creeped into them too.) Enochlau 01:41, 8 November 2005 (UTC)

Thanks! I may need to wait till this person's theory gets accepted by the scientific community before making further postings. Would anyone who has read the book by him or is actively engaged in atomic modeling theory give some comments. KJie.Neo 07:48, 8 November 2005 (UTC)
By someone else
There are no crack pot theories. Some theories are more correct in explaining some phenomenon until some other theory creeps up, which becomes more correct.
Hmmm, this theory seems rather far fetched to me. There are a few things to consider, firstly while it is true that electrons are far smaller than protons (about 1/2000th) it should be noted that the electrons cannot be attributed as point particles, or in fact as having a particular rigid shape. They are, for all intents and purposes of this explanation, a smear or cloud around the nucleus, thus the probability of interaction is not a simple matter of which particle is larger. Photons will have a hard time finding their way thru to the nucleus in the first place.
Secondly, If a nucleus was to be displaced what would cause the increase in the distance between the electron and the nucleus, The electrons would simply move with the nucleus, as per electrostatic forces, as the electrostatic force isn't reactive, i.e it is immediate. What would cause the electron to (essentially) stay in the same place (excuse the wording, an electron would never stay in the same place but for the sake of this argument...)
Thirdly, If the electron is emitted due to a change in displacement of the nucleus, then why would there be no dependence on the energy of the electron on the intensity of incident light? If the above theory were to hold, then there is no restoring force on the displaced nucleus, thus as more photons hit it will keep changing its displacement, and the greater change should then cause an electron with a higher binding energy to escape, which would mean the work function of the material would change with the intensity of the light as well.
Fourthly, if the electron simply escapes the bound of the electrostatic force (as this postulates) then why would the electron have a differing energy depending on the incident lights frequency. Surely all the electrons irrespective of the frequency, will have an energy coinciding with the bound state energy.
I could go on, but that will suffice. Pubuman 16:59, 10 August 2006 (UTC)
Since a single proton has a physical dimension of around 10E(-17)m, does it occur to you that an electron must have a physical dimension however small it may be? In fact, it is not that small considering that an electron has 1/1836 times the mass of a proton. Simple algebra would put the electron as having a physical dimension in the order of around 1/10 the physical dimension of the proton diameter if we consider the proton and electron as solid particles. If we consider it to be a hollow sphere, then the electron will be slightly smaller. In any case it will have a dimension not smaller than 10E(-19)m. The only problem is that our current instrument cannot measure the electron size accurately because the electron has another property that is governed by its spin. This property makes the measurement of the physical size of the electron extremely difficult. This is why no physicist is prepared to give the electron a physical dimension not because it has none.
Since an electron has a physical dimension, does it not occur to you that a proton that has a cross sectional area of roughly a 100 to a 1000 times that of an electron will have a greater probability of interacting with a photon that is fired at an atom? If that is the case, shouldn't the protons be a better candidate of interacting with a photon when it is fired at an atom?
If a proton inside the nucleus capture a photon, then this will essentially raise the rotational kinetic energy of the nucleus which commensurate with the amount of energy contain in that single photon. It will then cause the entire nucleus to rotate with a greater nuclear radius that varies with the photon energy. This will give rise to two effects simultaneously. At one phase of the orbital electron it will experience a stronger interactive electromagnetic force when it is in close proximity to the nucleus. At another it will experience a weaker interactive electromagnetic force when it is further away. The second phase of the electron rotation about the nucleus is the basis for the emission of a photo electron from the atom.
I am the author of the alternative theory to the explanation provided by Albert Einstein ie, the crack pot referred to by some of the contributors here.
—Preceding unsigned comment added by 116.15.46.111 (talk) 03:11, 12 April 2008 (UTC)

Photons or electrons ejected?

In the first paragraph in the 'Explanation' section, there's this sentence:

Increasing the intensity of the light beam does not change the energy of the constituent photons, only the number of photons ejected.

I'm not physicist, so it's likely that I'm mistaken; but it appears to me that it's electrons that are ejected, not photons. If I am correct, then (in addition to changing 'photons ejected' to 'electrons ejected') maybe some clarification is in order, regarding which or how many electrons are ejected (e.g., presumably not all from the same atom). I'm not changing anything myself because I'm too clueless about physics.

Amichai Schreiber 13:01, 16 July 2007 (UTC)

Thanks for pointing that out. enochlau (talk) 13:39, 16 July 2007 (UTC)

I now see that this was changed to electrons, then changed back to photons, and now the 'ejected' was removed too. Can anyone clarify? Amichai Schreiber (talk) 07:30, 1 July 2008 (UTC)

I've rewritten that sentence. Hopefully that makes more sense now, and I hope whoever is muddying it will let it be. enochlau (talk) 04:56, 2 July 2008 (UTC)

Wikipedia:Reference_desk/Archives/Science/2009_January_8#Light_as_waves_AND_particles

I do not contradict your quote. -lysdexia 02:47, 17 January 2009 (UTC) —Preceding unsigned comment added by 69.108.164.45 (talk)

Separation of different regimes

I think perhaps we have our article a bit jumbled. We could separate out the information relevant in the following regimes (or something similar):

  • General/all-inclusive
  • PE on metal and semimetal surfaces (visible to near UV to eject conduction band electrons)
  • PE on non-metallic liquid and solid surfaces (vacuum/extreme UV to soft X-rays)
  • PE in the interior of a solid/liquid (extreme UV through soft gamma rays)
  • atomic/molecular/gas-phase PE (i.e. photo-ionization)(mid-UV through gamma rays, giving rise to absorption spectrum with edges, etc.)

I am looking for suggestions regarding possible reorganization of the article in this way, given that many of the sections are only applicable in one or two or these regimes, and given that in a sense these are actually different phenomena. 69.140.12.180 (talk) 23:23, 21 May 2009 (UTC)Nightvid

Dubious sentence?

The sentence "Nonetheless, the notion that the photoelectric effect demonstrates the particle nature of light persists in many introductory textbooks" seems like a non-sequitur. According to the analysis of G. Araki, "QM of Circularly Polarized Photons," Prog. Theor. Phys. 1:4 125-142, 1946, photons express polarization as spin. A photon absorbed by an electron confers on it not just its energy but also its linear and angular momentum, which the electron then distributes to its neighborhood as needed in order to stay in its new orbit. Photons being bosons, their spin is integer; if it were half-integer as for fermions all light would be circularly polarized. The analysis in Schroedinger's December 1926 paper demonstrated twenty years earlier the necessity of such an exchange. Unless I've misunderstood Araki (always a possibility) he is merely explicating Schroedinger's analysis for this particular case. If there are no objections I will restate this sentence more appropriately. --Vaughan Pratt (talk) 12:59, 13 January 2010 (UTC)

In the meantime I read Lamb and Sculley's paper. The point it takes 15 pages to make can be seen as an immediate consequence of the Schroedinger paper I mentioned above.

A trap for young players in physics is that the literature is replete with incomplete, misleading, or just plain wrong accounts of phenomena. Some of it is written by very eminent physicists, the EPR paper being perhaps the best-known example but one that barely scratches the surface of the tip of the iceberg. Another example is the noted experimental physicist Robert W. Wood's famous refutation of the greenhouse effect in the February 1909 issue of Phil. Mag., promptly and comprehensively refuted in the July issue by no less than the director of the Smithsonian Astronomical Observatory, Charles Greeley Abbot yet cited today by at least half the climatologists on the planet as proof that the greenhouse effect has nothing to do with greenhouses, completely ignoring that the connection was demonstrated convincingly by Horace de Saussure in 1767.

If there are no objections I will simply replace this section with at most a remark somewhere to the effect that by wave-particle duality the effect can be analyzed purely in terms of waves though not as conveniently. --Vaughan Pratt (talk) 14:34, 13 January 2010 (UTC)

I don't think even that caveat is necessary. The Lamb-Scully paper is just plain wrong.--75.83.69.196 (talk) 05:04, 26 January 2010 (UTC)
Uh, ahem. The idea expressed by Lamb and Scully is correct, important and indispensable in the physics of today. Almost any good textbook on graduate-level quantum mechanics includes analyses of a quantum atom being perturbed by a classical field. Why? The calculations are enormously simpler than with a quantized field, and give the same answer anyway (with the exception of experiments measuring statistics of photoemission produced by exotic light sources which practically exist only in quantum optics laboratories!) Sakurai and Townsend, for instance, derive the ionization rate of an atom in a classical light wave in just a few pages - but any treatment with a quantized field will takes three times as long. What's the point? (And if you don't believe me, I challenge you to find a single one of the many good quantum optics books to prove me wrong!) 69.140.13.88 (talk) 14:58, 26 January 2010 (UTC)Nightvid
I also dare say that the single most important cornerstone of the field of quantum optics (QO) is that in fact the phenomena which are often claimed to demand a quantum description of light (and yes, this includes the photoelectric effect) in fact are fully explicable with only a quantum description of electrons in the matter upon which the light shines. There is a consensus on this point in quantum optics books. Please see [1] and references 5-7 therein. You are not about to refute the very important and painstaking work of many groups of physicists the experiments on photon antibunching which are necessary to prove photons exist! 69.140.13.88 (talk) 14:58, 26 January 2010 (UTC)Nightvid
Ok, so I misstated my concern: there are two dubious sentences, the one I brought up and the one preceding it that reads "It is also important to note that the particle nature of light cannot explain the dependence on polarization with regard to the direction electrons are emitted, a phenomenon that has been considered useful in gathering polarization data from black holes and neutron stars." My original and continuing complaint is that this sentence is false. Have you said anything that would contradict this? You yourself seem to be saying it is false when you say "and give the same answer anyway." And why do "exotic light sources" require an exception? --Vaughan Pratt (talk) 13:20, 30 January 2010 (UTC)

2010 Discussion - Other aspects of photoelectric effect that might be worth including

There are several aspects to photoemission that are not considered, such as the band model, electron affinity and how the kinetic energy imparted to an electron by the frequency of light is important to photoemission - as it defines whether the electron will be delivered to the conduction band or will move to the vacuum level at which point it can leave the material.

I've added some extra material here into the section on night vision devices, since it is relevant there, but it seems strangely absent from the rest of the article.

Electron affinity is not discussed at all, with respect to photoemision from the material of photoelectrons and the band model is rather pertinent to understanding the cutoff frequency of light that will result in a photoelectron emission.

Additional to this, there are the aspects of other losses in any photoelectric material. This is quite relevant to the thickness of the material.

Additionally, Band Bending is an important aspect of how, near the surface of a photoelectric material, the work function is significantly reduced ( or increased ) depending on the material.

Maybe this isn't the place for such information, but it is relevant. Any thoughts here? David. —Preceding unsigned comment added by 119.12.168.77 (talk) 09:36, 9 July 2010 (UTC)

Experimental results

Result no. 3: "For a given metal of particular work function, increase in frequency of incident beam increases the intensity of the photoelectric current."

Is there any experimental data on this? As far as I know, only the kinetic energy of the electrons increases with frequency. Judging by the formula of the cross section (end of article), the probability to create a photoelectron (and therefore the intensity of the photoelectric current) should decrease with f^(-3). 77.179.5.80 (talk) 16:40, 17 June 2010 (UTC)

Ok, it seems somebody split the above sentence into two separate statements on 11:38, 20 July 2010 without comment. I totally agree with the new Result no. 3: "For a given metal of particular work function, increase in intensity of incident beam increases the magnitude of the photoelectric current, though stoppage voltage remains the same.".

However, my initial concern is still valid for Result 4: "For a given metal of particular work function, increase in frequency of incident beam increases the maximum kinetic energy with which the photoelectrons are emitted, but the photoelectric current remains the same, though stoppage voltage increases.". I believe (but may be wrong) that, rather than "the photoelectric current remains the same", it should decrease with increasing frequency, because the cross section does so. 77.179.224.60 (talk) 17:03, 29 July 2010 (UTC)

Relativistic photoelectric effect

Some information concerning this aspect is better to be introduced into the article.--84.232.141.38 (talk) 18:34, 12 September 2010 (UTC)

Expand

...As Wtshymanski seems to like to do to Tesla's contributions, he deleted the following....

Radiant energy
Photoelectric motor. Rays falling on insulated conductor connected to a capacitor: the capacitor charges electrically.[1]

Nikola Tesla described the photoelectric effect in 1901. He described such radiation as vibrations of aether of small wavelengths which ionized the atmosphere. On November 5, 1901, he received the patent US685957, Apparatus for the Utilization of Radiant Energy, that describes radiation charging and discharging conductors. This was done by using a metal plate or piece of mica exposed to "radiant energy". Tesla used this effect to charge a capacitor with energy by means of a conductive plate, making a solar cell precursor. The radiant energy threw off with great velocity minute particles[2] (i.e., electrons) which were strongly electrified. The patent specified that the radiation (or radiant energy) included many different forms. These devices have been referred to as "Photoelectric alternating current stepping motors".[3][4]

In practice, a polished insulated metal plate or other conducting-body in radiant energy (e.g. sunlight) will gain a positive charge as electrons are emitted by the plate. As the plate charges positively, electrons form an electrostatic force on the plate (because of surface emissions of the photoelectrons), and "drain" any negatively charged capacitors. In his patent application, Tesla noted that as the rays or radiation fall on the insulated conductor (which is connected to a capacitor), the capacitor will indefinitely charge electrically.[1]

This should be put back in. --J. D. Redding 07:45, 15 December 2010 (UTC)

Why? Not every patent actually works. This scheme doesn't work and is irrelevant to a discussion of the photoelectric effect. Tesla either was clueless or else was deceptive in taking out a patent. It's not a solar cell, otherwise every galvanized roof in the world would be sparking over. Why did Tesla need to buy coal for Wardenclyffe if he could have just put a plate in the sunshine? (For that matter, why even bother with Wardenclyffe and wireless power transmission if a plate in the sun suffices?) Tesla himself, being a superb experimenter, realized this scheme doesn't work. We spend no time in the thermodynamics articles discussing the phlogiston theory. We should not waste the reader's time with historical dead-ends and crackpottery that has nothing to do with the modern understanding of the topic and which does not illustrate anything relevant to the topic. --Wtshymanski (talk) 14:59, 15 December 2010 (UTC)
No. It is the earliest example of photoelectric patents. It is classified as such also. --J. D. Redding 01:28, 16 December 2010 (UTC)[ps., oh, btw, it does work ... ]
Oh really? How about a reference? Where are the acres of sheet metal in the sun, collecting 'radiant energy' ? Tesla disciples seem to always come up short on results. Whatever the wacky physics Tesla had in mind, what he built isn't a photoelectric device. Find me a reference outside the cult who believes that ...thing...works and works on the photoelectric effect. --Wtshymanski (talk) 02:44, 16 December 2010 (UTC)
"Let me discount everything of the cult who believes", haha ... funny ... bordering on trolling. Psuedo-Skeptical disbelief is not called for.
The patent office classifies it was photoelectric device [need a ref link?] ... but i'd imagine the goal posts have been moved beyond that. Anyways ... i'll post some other links [non-scholarly and scholarly] later maybe for ya Wt... but that doesn't prevent the material being included. The patent office should suffice.
If you are so sure it doesn't work, then surely you can provide a references that it is not? Probably not [blah blah prove a negative blah] ... but seems that you should have alot of referencs that say it doesn't work ... bah ...
--J. D. Redding 06:33, 16 December 2010 (UTC)
It's not pseudo-skeptical disbelief, it's real disbelief. Tesla's contraption isn't a photoelectric device. It may have been a way of defrauding investors, nothing like a patent to bring in the suckers, but it doesn't make electricity. It doesn't belong in this article. Just because Tesla published some mystical half-baked speculation that has been cherished by the fringies for 70 years doesn't mean it belongs in a serious article that is intended to explain something to a general audience. Tesla was a brilliant man but more or less off his rocker after, oh, say, 1895. It's rather pathetic to imagine the newspapers, needing some copy to fill a hole, sending someone down to talk to the recluse and come back with some story about death rays and extraterrestrials. --Wtshymanski (talk) 14:34, 16 December 2010 (UTC)
Attacking the man does nothing to the facts and only weakens what you say. --J. D. Redding 05:53, 17 December 2010 (UTC)
Tesla's device works in principle. In practice, the atmosphere absorbs much of the UV needed to make this "sun motor" usefull, as they are required to knock off electrons from the metal. The photovoltaic effect, which is related but somewhat different, uses the band gap have a sort of "effective ionization" mechanism, which requires photons of ~0.1–1 eV instead of ~10 eV. The problem with the Tesla enthusiast is that their argument is more or less that since Tesla was a genius, all his ideas are good and achievable. Tesla was very often (but certainly not always) right on principles, and had a vivid imagination, but when these principles applied, reality's constraints made them non-viable.
I am unsure that this motor warrants significant coverage in this article. A dedicated article to Tesla's "sun motor" would be better IMO, and then we could have a link in the "See also" sectin. That would be the best solution I think. Headbomb {talk / contribs / physics / books} 06:52, 17 December 2010 (UTC)
Should have a brief section in the history and then, if needed, a WP:SUMMARY. J. D. Redding 12:34, 17 December 2010 (UTC) [ps., Tesla device can be operated by photoelectric and photovoltaic effects ... should be included there in the history.] [pps., ... the photon (a modern conception) hit the plate, naturally from the sun or from Wilhelm Röntgen's Röntgen tube or from Philipp Lenard's Lenard tube or a single-noded tube of Tesla's own design, and produced the effect of this article.]
No, it should not. Tesla's cartoon physics have no place in an article on the photoelectric effect. Tesla's thing was always ionic conduction in rarified gases - the plate in his gizmo collects ions, and is not emitting electrons as a photoelectric device would do. There's also no place on Earth with enough UV hitting the ground to make a cast-iron plate emit photoelectrons. Also, photoelectric devices operate in vacuum, not air. There's no mention of the work function, and no specification for the material of the plate, which is critical. If Tesla's device could work, every sheet-iron roof in the world would give off sparks on a sunny day. Tesla knew this didn't happen. I've no idea what his motives were for filing a patent on a device he must have known could not possibly work. I speculate his mental disorders, visions, etc. were affecting his work by this point and that's why he filed a useless patent; the other possible explanations I can think of are even less charitable. --Wtshymanski (talk) 14:19, 17 December 2010 (UTC)
Please stop editing with a POV, as seen by this comment. Thanks. --J. D. Redding 14:26, 17 December 2010 (UTC) [ps., did you miss the Röntgen tube and Lenard tube comment above? Or did your rage blind you?]

Favoring the facts is a point of view, yes. Have you read Patent 685597 lately? Specification, page 1,near 20, he's talking about ions flying through the air charging and discharging objects - a reasonable guess, but not the photoelectric effect. Near 60, he says the rate is very slow...so how can we get any useful power out of it? Near 80, he says he's "ascertained" (lovely word, by experiment or by intuition?) that the collecting rate is proportional to area. Doesn't give that rate for sunlight, of course. At 85 the surface has to be clean, highly polished, and amalgamated. What is the work function of mercury? Tesla didn't know or doesn't care, or knows and is hiding this information. Amalgamation was a standard technique for battery plates relying on *ions* to carry charge. Then there's a whole bunch of confusing text around 90 where he talks about connecting the condensor to a battery; later on he just grounds one side of his circuit.

The best part is around 100 of Specification page 1, wrapping over to page 2, where he says the streams of matter are generally *positively* charged. He's not even collecting cathode rays (electrons) with his amalgamated plate, he's collecting *ions*. This is not the photoelectric effect.

Specification page 2 near 45, he says sunlight radiation from the sun works. (Sure it does...as well as anything works in this patent). In 50 he says the sun throws off minute particles of *positively* charged matter...those aren't electrons, not in this part of the universe. Somehow these charged particles make their way through 15 pounds/square inch of air (same mass density as 4 feet of steel) only to alight on his insulated plate. Somehow these charged particles haven't blasted every living thing on Earth into a random soup of ionized molecules. In 65 he says this works so well that he can breakdown his mica capacitor! Really observed, or just in his mind's eye? And why doesn't his charge plate break down the air around it before the capacitor breaks down? Tesla doesn't say, either he doesn't know or doesn't care (or he knows and is hiding the information from his potential business partners). He then talks about some clockwork pawl and electromagnet system to collect the charge of the capacitor and put it to use; this would make a lovely solar clock, if it worked. He then goes on to talk about UV lamps and X-ray tubes illuminating the plate. In specs page 3 near 40, we discover the plate works equally well with + or - ions; again, this is not the photoelectric effect. In 60 he invents radio, communications lasers, and communications X-rays.

The patent disclosure is full and clear. Anyone skilled in the art can build one. Even the free energy ...enthusiasts...aren't building Tesla solar motors because they don't work even worse than the contraptions they do claim to build.

And it's NOT the photoelectric effect.It's claimed Road Runner physics is the exact *opposite* of the photoelectric effect.

--Wtshymanski (talk) 15:04, 17 December 2010 (UTC)

... the _key_ part of the preceding rant ... "He then goes on to talk about UV lamps and X-ray tubes illuminating the plate". Ah, the photoelectric effect! Röntgen and Lenard did the same thing.
But, but, but ... favoring your "facts" is a point of view, yes. Don't let your truth be wrong ... and AGAIN, I must state to you, attacking the man does nothing to the facts and only weakens what you say.
Here it is ... U.S. patent 685,957 - Apparatus for the Utilization of Radiant Energy
You missed this one though ... U.S. patent 685,958 - Method of Utilizing of Radiant Energy
These are related to one another [both patents] ...
Now, the line "The sun, as well as other sources of radiant energy, throws off minute particles of matter positively electrified, which, impinging upon the plate, communicate continuously an electrical charge to the same". Negatively charged energetic particles, they are "positively electrified" This was the understanding at the time. Don't obfuscate history. Year 1901. Only in 1901 did Planck began suggesting that the energy in electromagnetic waves could only be released in "packets" of energy.
But you seem to misconstrue what is said ... he's not collection "ions" ... and other slanting of the text is seen here with "highly polished *or* amalgamated." ... not 'and' ... damn my patience runs thin with the perversion of the text ...
As to ... "why doesn't his charge plate break down the air around it before the capacitor breaks down"? The condenser [capacitor] charges ... it takes the energy from the anode via the wire ... do I really have to explain this to you? Why don't you go build a crystal radio, you may 'ascertain' things like this ... really, do you understand any of it? or is "there's a whole bunch of confusing text"?
Unto ... Ascertained? by research ... unlike by 'Road Runner physicists' here ... Tesla had a well funded lab at the time [up to the turn of the century].
Going on to ... Testing by people today? There are people testing it ... look around for the amateur work concerning it [the best one I seen several months back was by a gentleman that isn't even exposing it to direct sunlight, just trying to receive natural EM waves]. But you wouldn't know because it's all 'wrong' to you, Wtshymanski... done by FE 'enthusiasts' only ... idiocy ...
Getting back to the patent, it's NOT the photoelectric effect ... though, the patent DOES utilize the photoelectric effect.
I would like to discuss the topic with other neutrally disposed editors. I don't think i can with you because of your POV.
Sincerely, --J. D. Redding 02:31, 18 December 2010 (UTC)

Tesla's Sun Motor

The following is from : Wireless telegraphy: its origins, development, inventions, and apparatus By Charles Henry Sewall ... pages 53 to 55.

Tesla's Sun-Motors — Fig. 15 and 16 illustrate other devices by the same inventor. These are called "apparatus for the utilization of radiant energy."

In Fig. 15, P is a plate exposed to rays, and P' a plate buried in the ground. C is a condenser, the plates of which should present as large a surface as possible, the inventor having ascertained the amount of energy conveyed to it per unit of time to be, under otherwise identical conditions, proportioned to the area exposed or nearly so. T and T' are terminals of condenser C. A relay magnet or any other device capable of being actuated by an electric current, d, may be composed of two very thin conducting plates placed in close proximity, and, either by reason of extreme flexibility, or from the character of their support, very mobile.

It will be seen that the magnet M, if energized and de-energized, will actuate armature a, and, with a pawl and ratchet movement, turn, one step at a time, the wheel W. When the condenser C is charged to a certain potential the dielectric between the strips will break down, and the condenser discharge its accumulated energy through magnet M. When the strain on the dielectric has been relieved the strips t f will resume their normal position.

The originator of this device says that "many useful applications of utilizing the radiations emanating from the sun, and many ways of carrying out the same, will at once suggest themselves."

Sincerely, --J. D. Redding 05:53, 17 December 2010 (UTC)

"Sincerely" is an interesting way to sign this. --Wtshymanski (talk) 15:12, 17 December 2010 (UTC)
Why? ... why do you care? Obvious troll is obvious. --J. D. Redding 02:31, 18 December 2010 (UTC)

found the patent with the writing on it

--J. D. Redding 03:22, 26 December 2010 (UTC)

Explaining the photoelectric effect without photons

There is no reference to the paper by Lamb and Scully, "The photoelectric effect without photons", which shows that you can describe the photoelectric effect by quantization of the metal atoms, with classical light. Any reason why? It seems like a pretty big hole in the article. 67.81.184.181 (talk) 01:45, 4 March 2009 (UTC)

The Lamb and Scully paper is wrong, and it was never published in a peer-reviewed journal. An analysis is given here http://www.lightandmatter.com/cgi-bin/meki?physics/faq#quantum_mechanics,Didn%27t_Lamb_and_Scully_show_that_you_don%27t_need_photons_to_explain_the_photoelectric_effect? The standard textbook treatment given in the article is correct.--75.83.69.196 (talk) 05:03, 26 January 2010 (UTC)
Stop spreading misinformation! It was indeed published in the French journal!
Polarisation, Matiere et Rayonnment, Presses University de France, 1969
P.S. A dot-com without references is not a reliable source!
129.2.175.70 (talk) 16:45, 26 January 2010 (UTC)Nightvid
"Lamb and Scully in 'The photoelectric effect without photons' (in Polarisation, Matiere et Rayonnment, Presses University de France, 1969) showed that one can account for the Ph.E without the concept of photons, and, thus, the Ph.E. does not provide proof of the existence of photons." --Gershenson, Mike (2009), "Lecture 4. Particle properties of waves". Dept. of Physics & Astronomy; Rutgers, The State University of New Jersey.
Scully, Willis E. and Marlan O. Lamb (1968), "The photoelectric effect without photons". Center for Theoretical Physics, Univ. of Miami.
Aristov, V. V. (2008), "The Photoelectric Effect in the Semiclassical Theory", DOKLADY PHYSICS Vol. 54 No. 4 2009. DOI: 10.1134/S102833580904003X.
I'm just posting reference material here; NOT taking sides. Cheers!, Rico402 (talk) 06:30, 27 January 2010 (UTC)
The lightandmatter.com faq is incorrect (among other things the author does not understand perturbation theory), the Lamb and Scully paper definitely has merit and the use of the Fermi Golden Rule for photoemission is included in any decent textbook on quantum mechanics. I am not sure how much of this information should be included in this article, but the current hand waving statement about "wave particle duality" (with a reference to Lamb and Scully!?) just confuses things. Maybe a new article on semiclassical quantum optics is needed? --95.103.205.238 (talk) 22:06, 4 January 2011 (UTC)

Photoelectrons or electrons?

Introduction

In the first sentence defining the photoelectric effect it says "photoelectrons are emitted". I propose that this be changed to "electrons are emitted" as the "photo" prefix is not necessary and may leave the reader wondering "what's so special about these photoelectrons?". As this is the first line of the article it is important to be succinct, but also I thought I would canvas opinion before changing it. Uberdude85 20:51, 11 March 2007 (UTC)

 Done: I completely agree with that change, and when I saw that it had already been changed I actually thought I was the one to do it (perhaps I did it in another article?). Brian Jason Drake 09:22, 15 October 2009 (UTC)


First sentence ==== Very short wavelenght====

In the photoelectric effect, electrons are emitted from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of == very short == wavelength, such as visible or ultraviolet light.

In my opinion this neither is a very good physical expression nor is ultra violet or visible light of very short wavelenght. I would suggest to take out the term "very" at least if it is not possible to find a better expression. "Specific" instead of "very short" would be more correct. mg 20.1.2011 —Preceding unsigned comment added by 128.131.207.13 (talk) 13:19, 20 January 2011 (UTC)

Image caption

I presume the first two comments in the #Introduction section were used to justify "rm (removing) photoelectrons" in the image caption "as per talk". I also agree with this change. For completeness, I note that the opposite change was previously made, with the edit summary, Edited the caption on the main image of the article. The emitted electrons are more correctly identified as photoelectrons." Brian Jason Drake 07:56, 16 October 2009 (UTC)

Stopping potential

I've included the stopping potential, it's a very important stuff. By the way I hope someone bans this guy Materialscientist, he's undoing my work. — Preceding unsigned comment added by 83.54.144.187 (talk) 09:07, 17 March 2011 (UTC)

X-ray diagnostic images are produced by photoelectric and Compton effects

which is likely the most common "use" of photoelectric effect nowdays. The lead of the article ("definition") clearly does not recognize this banal fact.--Ilevanat (talk) 01:16, 11 January 2012 (UTC)

Second paragraph of Emission mechanism

"Electrons can absorb energy from photons when irradiated, but they usually follow an "all or nothing" principle. All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or else the energy is re-emitted."

Is this generally true? From the context it seems that all interaction between photons and electrons follow the "all or nothing" principle. This is however not the case. For example Compton scattering, where an electron gain kinetic energy and the photon lose some, but not all, of it's energy. — Preceding unsigned comment added by 193.91.141.107 (talk) 09:32, 15 March 2012 (UTC)

probablity of ejection

I wanted to ask that if an electron absorbs a photon of energy 'e' which is greater than the work function, will the electron surely be ejected? Or is there some probability that the energy will just be re emitted? — Preceding unsigned comment added by 1.38.24.86 (talk) 16:51, 27 June 2012 (UTC)

Quanta is also known as Planck constant.

The subject sentence is found at the end of the second paragraph of the introductory section of the article and is confusing. In fact, the last two sentences:

"It also led to Max Planck's discovery of quanta (e=hv) which links frequency with photon energy. Quanta is also known as Planck constant."

should be rewritten to eliminate the ambiguity around the word "quanta". I suggest something like:

"It also led to Max Planck's discovery of quantized energy and the Planck Relation (E = hv), which links a photon's frequency with its energy. The factor h is known as the Planck constant."

with the appropriate hotlinks to other articles. Gzherka (talk) 10:45, 22 December 2012 (UTC)

Done. But you could have been bold, that was pretty poor. --Wtshymanski (talk) 21:37, 22 December 2012 (UTC)

Experimental apparatus?

It would be nice to have a diagram near the top showing the experimental apparatus used to detect and measure the effect. Presumably there is a photocathode and an anode, and some way to impose a voltage between them and measure the current with and without light of various wavelength striking the cathode? What is this "stopping voltage" and how is it measured? This could be right below the simple picture of photons striking a surface and electrons being ejected.Eaberry (talk) 19:48, 18 May 2013 (UTC)

Planck, h and photoelectric effect

Re"The photoelectric effect requires photons with energies from a few electronvolts to over 1 MeV in high atomic number elements. Study of the photoelectric effect led to important steps in understanding the quantum nature of light and electrons and influenced the formation of the concept of wave–particle duality.[1] Other phenomena where light affects the movement of electric charges include the photoconductive effect (also known as photoconductivity or photoresistivity), the photovoltaic effect, and the photoelectrochemical effect. It also led to Max Planck's discovery of quantized energy and the Planck Relation (E = hv), which links a photon's frequency with its energy. The factor h is known as the Planck constant."

"It also led to Max Planck's discovery of quantized energy". Not so. Plamck discovered his constant of action, h, in his resolution of the Black Body Problem. Later, Einstein used h in his solution of the photoelectric effect. ---- — Preceding unsigned comment added by 66.207.115.161 (talk) 19:03, 13 April 2013 (UTC)

Yes, I was reading the Planck Radiation article and found this conflict. It appears to me more logical that it is indeed this way: first Planck proposed said quantization as a mathematical instrument, akin to Boltzmann's, and established the relationship e=hv without relating it to the quantization of eletromagnetic fields, and only later when Einstein explained the photoelectric effect using quanta the two came together. In other words, Plank is the predecessor, although he did not envision quanta of light, while Einstein envisioned them and used Plank's discovery. 24.246.15.195 (talk) 07:23, 27 May 2013 (UTC)

reference 41 (Lamb and Scully)

This reference points to a page that does not have the article. Can you link to somewhere that does have the article? 66.17.49.210 (talk) 04:03, 18 July 2013 (UTC)Iuval

Nearby Plasma

What nearby plasma is this sentence talking about? "The photoelectric effect will cause spacecraft exposed to sunlight to develop a positive charge. This can be a major problem, as other parts of the spacecraft in shadow develop a negative charge from nearby plasma," I thought it may be referring to the light itself, but that is not a plasma. 76.198.38.250 (talk) 20:09, 20 July 2013 (UTC)

Merge discussion

It appears that photoelectric efficiency only discusses a small aspect of the photoelectric effect (especially since the other article uses "photoelectric effect" as the bold text at the beginning of the article). Although the precise effect mentioned in the article might not be treated specifically in this article, I believe merging relevant extra information would be preferable to keeping the other stub, especially since it has been an orphan since 2009. Azaghal of Belegost (talk) 00:31, 9 January 2014 (UTC)

Wave Theory of Light Can Explain Photoelectric Effect

Photoelectric effect can take place only when the incident light has a frequency above a certain threshold frequency.
Photoelectric emission for a metal takes place only if the light has a frequency above a certain threshold frequency which is an intrinsic property of the metal. This can be accounted for by the wave nature.As frequency increases, wavelength decreases as they are inversely proportional to each other.Therefore the energy carried by a ray of light is transferred to a smaller area if the frequency is increased.Every atom has a definite atomic radius. For the energy of the ray to be transferred completely to an atom, the area of the source should be equal to or lesser than the atom. Therefore a wavelength lesser than or equal to the diameter of the atom is required to trigger photoelectric emission.

Photoelectric effect is instantaneous.
The time required for one electron to break free of coulombic force from the nucleus is 10-9sec or less which can be accounted as the time taken for the energy transfer to take place.

Increase in Intensity is directly proportional to the photoelectric current.
Increase in Intensity of light can be assumed as increase in the no. of point sources of light. Hence a larger no. of atoms in the illuminated region are exposed to the light. This increases the no. of electrons released as a larger no of electrons gain energy. This also accounts for the saturation current as at a certain intensity, for a fixed frequency, the no. of electrons that can be released by the metal becomes constant and further increase in intensity has no effect.

The kinetic energy of photoelectrons increases with increase in frequency.
Increase in frequency leads to lower wavelength implying the energy has been transferred to a lesser area.Hence the electrons that are exposed to the radiation gain greater energy in the same time.

The Stopping Potential Is Proportional To The Frequency Of Incident Light.
Greater frequency of light means greater kinetic energy of the electrons. Hence force required to oppose the flow of electrons is also greater. Therefore an increase in stopping potential is observed.--Shreyasajitrajendran (talk) 08:20, 12 September 2014 (UTC)

Does electron emission rate depend on wavelength in the classical picture?

In my understanding, in classical electromagnetic theory the energy transferred by the light to the electrons is independent of the light's wavelength. As a consequence, the same is true for the electron emission rate. Murarrtexer (talk) 12:09, 23 October 2014 (UTC)

Vacuum?

Resolved
 – "Apparently extraneous" wording removed. Brian Jason Drake 09:12, 15 October 2009 (UTC)

Could someone please check the veracity of "vacuum or extreme ultraviolet".

I am confident ultraviolet causes Photoelectric effect, but a "vacuum"?

Thanks. —Preceding unsigned comment added by 66.81.112.103 (talk) 20:58, 12 October 2009 (UTC)

Apparently extraneous "vacuum or" deleted (at least until someone can explain what the heck they're talking about). Cheers, Rico402 (talk) 13:48, 14 October 2009 (UTC)
I agree; that phrase makes no sense. It seems to have orginated with revision 290363503. Brian Jason Drake 09:12, 15 October 2009 (UTC)

"Vacuum Ultraviolet" is what it meant. Referring to UV to which the atmosphere is not transparent. Bubsir (talk) 05:22, 3 February 2015 (UTC)

Add examples section

Please explain what stopping voltage is

The first time in the article the term "stopping voltage" is used is in the sentence "Thus the stopping voltage increases.". Please explain what it is before this sentence. — Preceding unsigned comment added by 213.151.48.138 (talk) 10:04, 14 June 2015 (UTC)

In Diagram of the maximum kinetic energy as a function of the frequency of light on zinc, frequency should be 10.4 instead of 10,4. Please check and found mistaken, correct it. — Preceding unsigned comment added by Neel doshi09 (talk • contribs) 08:47, 9 July 2015 (UTC)

Two questions a good A-level student might ask

1. Are we dealing purely with interactions between photons and conduction electrons? Not clear.
2. Why is it the maximum electron kinetic energy that figures in the discussion? Not explained.
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This is photovoltaics, not the photoelectric effect

The discussion above, and the page we are discussing, is principally focused on photovoltaics, which is only one application of the photoelectric effect.

The photoelectric effect is actually the explanation for the phenomenon observed by Max Planck, wherein light of specific chroma ie wavelength, ie frequency, were emitted in certain conditions by certain substances.

This was found to be due to transitions in state of electrons held by atoms/molecules being examined.

Photovoltaics involves the entire free-ing of the electron, and the converse aborption of a free electron. But photoelectric effect covers those interactions, as well as the smaller transitions of state of an electron in orbit, where it remains in orbit at all times, and merely jumps from one level to another.

Please correct me if I'm wrong, or if I'm right, and I know I'm right, please help to repair the article.

It's not that the article has entirely bogus info, just that the focus is on a small part of the actual phenomenon, a part which has its own name as well. -- Yabbadabbadoo 13:38, 17 October 2006 (UTC)

I don't think that's correct - all my references say it's just the emission of electrons as described in the article. Can you provide a reference - website or book that supports what you said? enochlau (talk) 01:11, 18 November 2006 (UTC)

The issue of history also is of importance here. Alexandre Becquerel is mentioned as observing the photoelectric effect but is not credited with its discovery. It stands to reason that if an individual observes and describes the effect for the first time then he or she is the discoverer of the phenomena. Hertz's work helped develop the understanding of the effect but he should not be credited as the discoverer of the phenomena especially since Becquerel and his father are credited with the discovery in the wikipedia article on the photovoltaic effect. This needs to be clearly explained to avoid the confusion not only of the concepts themselves, but of the history of their discovery.

Got references? enochlau (talk) 00:54, 16 February 2007 (UTC)

i was reading the "Photovoltaic module" and it said... "...to generate electricity through Photo-Voltaic effect (not to be confused with photo-electric effect)". how ever when i searched for the Photovoltaic effect i got redirected to the photo electric effect as if they were the same thing... are they different? -will- —Preceding unsigned comment added by 219.89.104.202 (talk) 09:54, 4 May 2009 (UTC)

Photoelectric and photovoltaic are largely the same thing. I'd say the main thing that distinguishes them in popular use are whether the emission is into another medium at a boundary or into the same medium. In practical terms, I think it comes down to whether the electron is transported away ballistically or diffused, since that determines whether the resulting energy available is proportional to the photon energy or not. If you get ballistic transport, you can get all the kinetic energy out of it, but once it diffuses, your usable potential is limited by the potential of the diffusion barrier. I suppose you could look at PE as just being the first part of the photovoltaic process though, prior to any concerns about how you get the energy out of the carrier. I don't think there's any sharp consensus in the usage other than that photodiodes are usually called photovoltaic and boundary emissions are usually called photoelectric, and personally I think the ballistic/diffusive difference is really where the split is, like photoemission belongs to the particle world and photovoltaic belongs to the entropic macro-world, kind of like energy vs. temperature. I had an argument about whether carrier photoexcitation alone counts as "internal photoemission" in grad school once, but I see people using it both ways. These guys clearly think it's the same thing as photoexcitation http://www.nature.com/ncomms/journal/v4/n3/fig_tab/ncomms2577_F2.html Another guy says "Internal photoemission (IPE), a process involving optical excitation of hot carriers in the contacts followed by transport across internal system barriers, is dominant when the molecular component does not absorb light." http://pubs.acs.org/doi/abs/10.1021/ja511592s , but then you'll also hear people doing hot carrier cells call them "photovoltaics". As for "photoelectric" vs. "photoemission", I've never heard "photoelectric" used much outside of historical discussions. I don't think it's very current in physics. Tarchon (talk) 00:57, 6 May 2016 (UTC)

  1. ^ a b N. Tesla "Apparatus for the Utilization of Radiant Energy" U.S. patent 685,957 (1901)
  2. ^ U.S. patent 685,957
  3. ^ This phrase was handwritten on one in a series of patents covering this effect. Tesla had several patents utilizing this effect.
  4. ^ U.S. patent 685,957
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