Wikipedia talk:WikiProject Physics/Archive August 2018

My several hours of major improvements to thermal resistance page just undone. Do I have support in undoing the undo?

See the bottom of its talk page here: http://en.wiki.x.io/wiki/Talk:Thermal_resistance -- ERCaGuy (talk · contribs) 17:57, 3 August 2018‎ (UTC)

Suggestion for a better name: Orbital angular momentum of free electrons

The article Orbital angular momentum of free electrons is weird to me, as it seems to imply that electrons as free particles may carry angular momentum apart from their spin. Do you have any idea what this phenomenon is about and to what name can we move it? MaoGo (talk) 15:03, 12 June 2018 (UTC)

OAM is a well-established concept associated with vortex beams; there is angular momentum associated with the topological vortex. See optical vortex, vortex laser beam, and orbital angular momentum of light for the optical analog. OAM for free electrons is more recent, but it has been established in the literature. I don't think there is a more common name for it. --Mark viking (talk) 16:42, 12 June 2018 (UTC)

There is nothing strange about it. It is just classical angular momentum. If the electron is moving on a line which does not pass thru the origin of the coordinate system, then it has angular momentum equal to the cross product of its position and its linear momentum. This is called "orbital" (i.e. depending on the trajectory or orbit of the particle) to distinguish it from the purely quantum mechanical "spin".

It turns out that it is also quantized in units of $\hbar$; always being an integer multiple of that unit. Whereas spin may be a half-integer multiple (but differences in spin are always full integer multiples). JRSpriggs (talk) 05:25, 13 June 2018 (UTC)

You are misunderstanding spin, if you think that all angular momentum is spin. JRSpriggs (talk) 05:51, 13 June 2018 (UTC)

In an atom, taking the location of the nucleus as the origin of the coordinates, the orbital angular momentum of an electron is described by the l and m quantum numbers. While the spin is described by the s quantum number. l is related to the eigenvalue of the total (magnitude) of the orbital angular momentum. m is related to the eigenvalue of the component of the orbital angular momentum parallel to an imposed magnetic field (or any other arbitrarily chosen direction). While these quantum numbers are usually used in the context of an atom, one could apply them relative to any coordinate system and use them to describe free electrons. JRSpriggs (talk) 08:57, 13 June 2018 (UTC)

If I understand this right, this article talks about a phenomenon that may only happen for a beam of electrons? I mean surely the article is not talking about an electron in a magnetic field. My problem is that angular momentum can be defined for free electrons in metals (see Landau diamagnetism) or for electrons in a cyclotron, or plasma or whatever. That's ok, but this phenomenon is about a specific case where we talk about a beam and I think a difference should be made more explicitly.MaoGo (talk) 09:24, 13 June 2018 (UTC)

Maybe we may change it to Orbital angular momentum of electron vortex beams MaoGo (talk) 09:31, 13 June 2018 (UTC)

We may also change its name to Electron vortex beam as it is already a redirect to it. MaoGo (talk) 12:18, 13 June 2018 (UTC)

I think "orbital angular momentum of electron vortex beams" is the least ambiguous title. XOR'easter (talk) 14:40, 13 June 2018 (UTC)

After taking my time to read the article and the sources, I think the article speaks about electron vortex beam, and not so much about the quantization. I think it should be called Electron vortex beam. MaoGo (talk) 08:42, 15 June 2018 (UTC)

I agree that Orbital angular momentum of electron vortex beams is the best title. orbital angular momentum is the major feature of this type of this type of electron beam. --Mark viking (talk) 17:55, 17 June 2018 (UTC)

This is incorrect, but is a common misconception. A single electron can carry quantized orbital angular momentum, as the free-space Hamiltonian and L_z commute. It is also true, as JRSpriggs noted above, that classical beams of electrons can carry orbital angular momentum, but this is actually not quantized in units of $\hbar$. The expectation value of orbital angular momentum is not necessarily quantized, as a free electron can exist in a superposition of multiple orbital angular momentum states, and the classical orbital angular momentum a beam of many electrons is just the sum of the expectation values of each electron.Tyharvey313 (talk) 10:36, 2 July 2018 (UTC)

I just made the bold move of making the move from OAM of free electrons to Orbital angular momentum of electron vortex beams. --MaoGo (talk) 11:59, 18 June 2018 (UTC)

This title is redundant. I would argue that there are two possible names for this article: either "electron vortex beams" or "orbital angular momentum of free electrons", and I chose the latter to be consistent with orbital angular momentum of light. All electron vortex beams carry orbital angular momentum, so the current title is the equivalent of something like 'depression of depressed people'. It makes much more sense to title an article 'depression in people'. It is also true that all free-space electrons can carry orbital angular momentum. I'm going to revert the title. I think just electron vortex beams could be fine, but again, I chose the title to be consistent with another article on parallel phenomena.Tyharvey313 (talk) 10:36, 2 July 2018 (UTC)

I propose to continue the discussion here if necessary. --MaoGo (talk) 13:19, 2 July 2018 (UTC)

The change is wrong. The original title Orbital angular momentum of free electrons is correct. Xxanthippe (talk) 03:39, 21 July 2018 (UTC).

@Xxanthippe: you have answered twice to this matter with this comment, why do you think the title is correct? --MaoGo (talk) 08:25, 6 August 2018 (UTC)

Twice? I onle see once. JRSpriggs has explained it well enough. Xxanthippe (talk) 08:35, 6 August 2018 (UTC).

@Xxanthippe: You declared the same thing is the talk page, I still believe electron vortex beams is a more simple and clear title. I just added a theory section to make the subject more clear, if you may, take a look. --MaoGo (talk) 09:27, 6 August 2018 (UTC)

Wiki Education hiring an experienced Wikipedian

Wiki Education is hiring an experienced Wikipedian for a part-time (20 hours/week) position. The focus of this position is to help new editors (students and other academics) learn to edit Wikipedia. The main focus of the position is monitoring and tracking contributions by Wiki Education program participants, answering questions, and providing feedback. We're looking for a friendly, helpful editor who like to focus on article content, but also with a deep knowledge of policies and guidelines and the ability to explain them in simple, concise ways to new editors. They will be the third member of a team of expert Wikipedians, joining Ian (Wiki Ed) and Shalor (Wiki Ed). This is a part-time, U.S. based, remote or San Francisco based position.

We are especially interested in people with experience editing physics-related articles. See our Careers page for more information. Ian (Wiki Ed) (talk) 20:10, 6 August 2018 (UTC)

Thomas-Fermi approximation

Are these two articles: Thomas-Fermi approximation and Thomas–Fermi approximation for the degeneracy of states, related to either Thomas-Fermi model or to Llewellyn Thomas? To me this two calculations are standard grand canonical ensemble calculations for a gas of either classical particles, fermions, or bosons. Also where is the approximation? --MaoGo (talk) 09:31, 8 August 2018 (UTC)

Ok the approximation is that you approximate a large integer number of particles as if it was a continuous distribution. Is this usually attributed to Thomas-Fermi? --MaoGo (talk) 13:18, 8 August 2018 (UTC)

The Thomas Fermi approximation assumes that the energy of a quantum system is large relative to the spacing of the energy levels. In this case a sum over energy levels, as in a grand canonical partition function, can be approximated by an integral; it's a continuum approximation. So even in a Bose-Einstein system with many particles, it is a poor approximation with system energy near the ground state. As I understand it, the approximation is used in the Thomas Fermi model; the sum over discrete quantum states inside a ball of a given radius is replaced with a continuum function. There are other approximations in that model, too, such as neglecting interactions and exchange energy--density functional theory is better for handling these. --{{u|Mark viking}} {Talk} 17:33, 8 August 2018 (UTC)

Should we keep the name of those sections as Thomas-Fermi approximation? It seems a rather general step to make. Also maybe Thomas-Fermi approximation should point to Thomas–Fermi approximation for the degeneracy of states and not Bose gas. --MaoGo (talk) 13:39, 9 August 2018 (UTC)

Plasma fusion preface

Plasma fusion preface looks like notes someone made for themselves while reading up on plasmas and fusion. Most of these look like textbook derivations and stuff that could be found in other articles, and it isn't clear as to where this article is going with its content. It also looks like there is a single major contributor and there may be a possible conflict of interest. I'm not sure what the best way is to clean up this article, what do other people think? -- AquaDTRS (talk) 17:01, 11 August 2018 (UTC)

It's been an orphan since '14. They've done something similar at Draft:Relativistic Energy Visualisation, and honestly I think it could be deleted without preamble. Primefac (talk) 18:00, 11 August 2018 (UTC)

In the draft catheters in a triangle. What does that mean? Both could be prodded. Xxanthippe (talk) 22:34, 11 August 2018 (UTC).

It's the name for the leg of a triangle. Primefac (talk) 22:47, 11 August 2018 (UTC)

Thanks, that's new to me. Not the same as catheter though. I still support prods. Xxanthippe (talk) 23:02, 11 August 2018 (UTC).

Indeed, I'd never heard the term before either (and I teach this stuff!). Primefac (talk) 23:02, 11 August 2018 (UTC)

Thanks. I've submitted the article for prod -- AquaDTRS (talk) 04:56, 12 August 2018 (UTC)

The prod was removed. I listed the article for AFD. Discussion at Wikipedia:Articles_for_deletion/Plasma_fusion_preface.--Srleffler (talk) 03:56, 16 August 2018 (UTC)

Relativistic Energy Visualisation may also need some attention.--Srleffler (talk) 02:42, 16 August 2018 (UTC)

It is not up to Wikipedia standard. Xxanthippe (talk) 02:47, 16 August 2018 (UTC).

Nonsense

As far as I understand, an anon is inserting a nonsensical "Vector Nuclear of Photon Released" to many articles. He is pushing his "theory" presented here, here and here (signed by Bilal Mohamed). His IP numbers: 196.224.17.232, 197.28.160.228, 197.28.165.239. Boris Tsirelson (talk) 13:46, 20 August 2018 (UTC)

See Talk:Path-ordering#Contribution of 196.224.27.85 and Wikipedia talk:WikiProject Mathematics#Nonsense. Boris Tsirelson (talk) 19:54, 22 August 2018 (UTC)

Oersted's law and Ampère's law

The article Oersted's law describes the concept that "electric currents create magnetic fields" as an important law named after Hans Christian Ørsted (thus an eponymous law name I've never heard of) and it is described as it is the same as Ampère's circuital law (it states that Oersted law is a Maxwell equation and it is written mathematically as Ampère's). Ampere's law article does not link Oersted law. I think a clear distinction between Ampère's law and Oersted has to be made but I don't know which. Some thoughts on the matter were given by an IP on Talk:Oersted's law. --MaoGo (talk) 14:03, 28 August 2018 (UTC)

Please review this draft

Could somebody look at Draft:Quantum Dimer Magnet and review it? It's quite technical. -- RoySmith (talk) 20:54, 28 August 2018 (UTC)

References to Johan Hansson's work

A Sweden-based IP at Lulea Tekniska Universitet is adding inline references to work by Swedish Johan Hansson in various articles. This looks like a wp:COI to me.

See 130.240.85.120 (talk · contribs · deleted contribs · logs · filter log · block user · block log). Can someone have a look at this and remove where inappropriate? IP notified and invited to comment here. Thanks. - DVdm (talk) 12:55, 30 August 2018 (UTC)

Thanks XOR'easter already. - DVdm (talk) 20:06, 30 August 2018 (UTC)

History of electromagnetic theory

... is one of the worst articles on my "to-do" list and has to be one of the worst main stream Wikipedia articles out there. It was massively expanded over several years by a primary source warrior who simply copied/pasted the 1918 Encyclopedia Americana and a series of turn (of the last) century articles and publications. And when they didn't do that they used primary source OR of published material dating back many centuries. If anyone has any suggestion for cleaning out this Augean stable (or wants to take a whack at it) feel free. Fountains of Bryn Mawr (talk) 21:49, 26 August 2018 (UTC)

Come, come, although verbose, it's not all that bad. Xxanthippe (talk) 22:36, 26 August 2018 (UTC).

• "The "open" cells are used very extensively at present, especially in the dry cell form, and in annunciator and other open circuit signal systems."
• the ultimate results of Heaviside's work includes uniting "Teslaic phenomena and Hertzian phenomena"
• "The AC induction motor helped usher in the Second Industrial Revolution"
• "When, however, in 1918 one views the vast applications of electricity to electric light, electric railways, electric power and other purposes (all it may be repeated made possible and practicable by the perfection of the dynamo machine), it is difficult to believe that no longer ago than 1871 the author of a book published in that year, in referring to the state of the art of applied electricity at that time, could have truthfully written: "The most important and remarkable of the uses which have been made of electricity consists in its application to telegraph purposes"."

Are we reading the same article? Fountains of Bryn Mawr (talk) 01:24, 27 August 2018 (UTC)

It's pretty bad. XOR'easter (talk) 20:10, 28 August 2018 (UTC)

Curate's egg clean up rather than TNT. Xxanthippe (talk) 22:46, 30 August 2018 (UTC).

Draft:Spectroscopy of Multiply Ionized Atoms

A review of this draft is requested. Should it be accepted as an article? Robert McClenon (talk) 15:46, 31 August 2018 (UTC)