Talk:Magnetic vector potential

message: I've never heard of "magnetic potential" as defined in the opening paragraph of this article, sounds very dubious. The vector and scalar magnetic potential formulations seem correct, but the article also lacks sources and is written in an informal tone. Let's clean it up and get an expert on this page. RyanC. 12:05, 7 March 2007 (UTC)
replies: text: And who would be doing this referring of the A-potential as unphysical? I'm not aware of any physics text written in the least 50 years that says that.Constant314 (talk) 22:54, 28 March 2013 (UTC)
replies: text: For starters, my quantum electrodynamics professor. --70.79.150.161 (talk) 02:54, 29 March 2013 (UTC)
replies: text:  Does your prof refer to A as unphysical or does he say that others refer to it as unphysical?Constant314 (talk) 04:04, 29 March 2013 (UTC)
replies: text:  Prof did. From the point of view of QED in particular, A simply sets the behavior of the force carrier and if you have zero mass, there's the photon. In terms of classical ED, it is used to set the gauge for the field equations but does not have a physical meaning outside of being used to give the form of the B-field. Thus my understanding that at least some E&M texts follow this pedagogy. --70.79.150.161 (talk) 04:26, 30 March 2013 (UTC)
replies: text: In the text (all classical E&M) books that I have, -dA/dt is responsible for the electric field produced by currents.  It is the principal actor responsible for transformer action with B relegated to causing skin effect and proximity effect.  If you have perfect conductors, you go from J (current density) to A to E without ever computing B.  To me, that makes A physical, or at least dA/dt is physical.  Feynman in volume 2 of his lecture series does a fine job of explaining this.  I have seen H referred to as unphysical because H would operate on magnetic monopoles, of which there are none.  Feynman has a special definition of a "real field" which is a set of numbers, local to a point, that allow you to calculate all the forces on the particle at that point.  The electric scalar potential and the A potential taken together, satisfy this requirement.  If your prof says A is unphysical, he probably has a specific technical definition for physical.  It is probably more productive to ask him why he says A is unphysical can to try to get the answer here.  On the other hand, it would not surprise me for the prof of a QED class to declare all fields to be unphysical.Constant314 (talk) 16:25, 30 March 2013 (UTC)
thread_title: Untitled

message: More explanation is good and more references are good, but 74.102.181.37 has added lots of new material including new concepts such as Decoupling Maxwell's Equations and four-dimensional potentials. This makes an already difficult subject, even more difficult to understand. My suggestion is that anything four dimensional should be given a separate article. Also, this is about the MAGNETIC potential so any reference to the ELECTRIC field should be minimal. Some simple magnetostatic examples using the magnetic vector and magnetic scalar potential would be nice (with diagrams even). Yes, there's more to life than magnetostatics but a reader is unable to learn the whole of physics in a single sitting... an article must be simple enough to be approachable and ultimately that implies deferring more complex concepts to other articles.
Possibly some references from the Maxwell's Equations page could be used here. Possibly also the material on the Maxwell's Equations page could benefit from being better organised. There must be text books covering magnetostatics surely?
:I think you're right. The part on "Decoupling Maxwell's Equation" may be better moved - though it's one main motivation for using the magnetic potential. The magnetic field B is more intuitive, but harder to deal with mathematically, that's why A is used. The stuff on "Four Dimensional potential" seems like it should also be moved off to electromagnetic potential. And "Reality of potential fields" needs to be improved/removed. 74.102.181.37 02:15, 13 June 2007 (UTC)
thread_title:  Too much material 

message: I propose that this article be split so that the magnetic scalar potential and magnetic vector potential are in different articles. Putting them both in the same place, at least as it's done now, ends up sorta implying that each is equally valid and equally widely used, when really the magnetic vector potential is way more important. Moreover, there's virtually no overlap between the two topics, and you can understand either of them perfectly without ever having heard of the other. Thoughts? --Steve (talk) 20:26, 21 July 2008 (UTC)
replies: text: Support gOOd idea. David J Griffiths's 3rd edition supports what Steve is saying. Pages 234-246, 252 describe quite a bit about magnetic vector potential, while magnetic scalar potential is only mentioned in passing. --Firefly322 (talk) 15:05, 22 July 2008 (UTC)

text: Weak Oppose If the term 'magnetic potential' is used for both then I prefer to use one page to include both for now.  With the lengths of the 2 sections as they are now, I believe it is slightly better to have magnetic vector potential point to Magnetic potential#Magnetic vector potential then to create an disambig page for magnetic potential.  This way the scalar vector potential may get more attention.  Plus, I hate disambig pages since they add extra clicks.  It is easy enough to point out that the magnetic vector potential is much more useful in the article.  If on the other hand the magnetic vector potential section grows to something approaching its stature in physics then it may need to be separated out. TStein (talk) 05:47, 26 July 2008 (UTC)
replies: text: I guess I was inclined to believe that "magnetic potential" isn't actually used for both. But after google-searching, I see that it is. (In physics "magnetic potential" always means vector, but in other disciplines like geology it often means scalar). So under those circumstances I'll agree that, until the page is longer, it need not be split. --Steve (talk) 05:16, 29 July 2008 (UTC)
thread_title:  Propose split 

message: I need to have the equations for A and phi for an article on transformers.  This article seems like the perfect place to put them.
I'll start by adding some references so they will be there when the new section is inserted.
And speaking of references, I have Jackson third edition in my hands and it says copyright 1999 instead of 1998.  Of course that doesn't mean there isn't a third edition out there with a 1998 copyright.  I think I can add a reference that is the same except for the year without breaking anything, so I'll just add a refernce that says 1999.  I'll leave it to someone else to delete the 1998 version if they are sure there is no such version.  
Constant314 (talk) 01:50, 2 November 2010 (UTC)
replies: text: In principle I think the equations for A and phi in the Lorenz gauge should be primarily in the Lorenz gauge article (which they're not right now, instead the formulas were split off into a separate article retarded potential), the formula for A and phi in the Coulomb gauge should be primarily in the Coulomb gauge article (right now Coulomb gauge is a section not an article, but the equations are there), etc. They should be here too, in all those forms, but perhaps discussed more briefly. :-) --Steve (talk) 20:26, 3 November 2010 (UTC)
thread_title:  Calculation of potentials from source distributions 

message: The first sentence says "In electromagnetism the physical effects can be expressed by either fields or potentials"
Aren't the potentials also fields? Constant314 (talk) 15:04, 3 November 2010 (UTC)
replies: text: I rewrote to clarify... --Steve (talk) 20:21, 3 November 2010 (UTC)
thread_title:  First sentence use of "fields" 

message: I have a depiction of the A field around a toroid shaped inductor for another article.  I think it could be useful here.  The lines are just drawn to look good and impart general look of the A field.  Constant314 (talk) 21:46, 20 November 2010 (UTC)
replies: text: Looks good to me. :-) --Steve (talk) 23:33, 20 November 2010 (UTC)
replies: text: thanks for the feedback and the edits.Constant314 (talk) 13:44, 21 November 2010 (UTC)

text:  I see you added that the depiction was for the columb guage instead of the Lorenz gauge.  Can you tell why it is one and not the other?Constant314 (talk) 14:06, 21 November 2010 (UTC)

text:  And are the two gauges are the same because the charge distribution is zero? I suppose I ought to mention that.  I suppose I should also mention quasi-static assumption? Constant314 (talk) 20:36, 21 November 2010 (UTC)

text: I think that I will change the caption to say div A = 0 is assumed then on the side say why that might be so.  —Preceding unsigned comment added by Constant314 (talk • contribs) 17:04, 22 November 2010 (UTC)
thread_title:  Depiction of the A field 

message: The author of one of the references reads "Davd" instead of "David"  — Preceding unsigned comment added by 18.51.3.219 (talk) 02:26, 22 November 2013 (UTC)
thread_title:  Reference is wrong 

message: Is the diagram in this section correct?  Martin Hogbin (talk) 15:44, 27 February 2014 (UTC)
replies: text: There is a long history of using dots and crosses for this purpose.  The crosses are interpreted as the tail feathers of the arrows entering the figure and the dots are interpreted as the tip of the arrows emerging from the figure.Constant314 (talk) 00:30, 28 February 2014 (UTC)
replies: text: I have seen that usage for the electric field, that is what first confused me before I read the section more carefully, but I have not seen it used for a magnetic field before. Three respected text books that I have to hand do not use that convention and this search does not seem to show it being used for the magnetic field, although it does show that usage for the electric field/current. It may seem rather old fashioned but what is the objection to using N and S? This makes it immediately apparent to most people that we are showing a magnetic field. Martin Hogbin (talk) 09:52, 28 February 2014 (UTC)
replies: text: Dots and crosses can be used for any vector field.  I don't think N and S would convey which was in and which was out.  Also, what would N and S mean when there was no obvious pole?  This is just lines of flux running in a circle around an axis.  Time Harmonic Electromagnetic Fields by Harrington and Principles of Radar by M.I.T. Radar School Staff both use dots and crosses for H field and E field depending on the point of view.  I've never seen N and S used for this purpose.Constant314 (talk) 00:40, 1 March 2014 (UTC)

text: Also Lectures on Physics by Feynman uses dots and crosses for the B-field in figure 23-16 of volume 2.Constant314 (talk) 00:57, 1 March 2014 (UTC)
replies: text: Yes, you are right Feynman does use it in one place. Martin Hogbin (talk) 10:02, 1 March 2014 (UTC)
replies: text: Regarding those three respected text books: do they have any depiction that has B or H flux going directly into the page or coming directly out of the page?  If yes, what convention do they use? Constant314 (talk) 17:40, 1 March 2014 (UTC)
replies: text: I could not find any examples where the magnetic field direction going into the page was shown, but I should say that one of the books was Feynman, so maybe I did not look hard enough. Martin Hogbin (talk) 21:14, 1 March 2014 (UTC)
thread_title:  Depiction of the A field 

message: Substituted at 22:50, 29 April 2016 (UTC)
thread_title: Assessment comment

message: An editor has asked for a discussion to address the redirect Tesla-metre. Please participate in the redirect discussion if you wish to do so.  signed, Rosguill talk 17:25, 8 April 2020 (UTC)
replies: text: I suppose Tesla-metre is a metre that measures magnetic flux density.  Perhaps it should redirect to Magnetometer. Constant314 (talk) 17:54, 8 April 2020 (UTC)
thread_title:  "Tesla-metre" listed at [[Wikipedia:Redirects for discussion|Redirects for discussion]] 

message: === Depiction of the A-field ===
Since 
\nabla \times \mathbf{B} = \mu_0\mathbf{J}
assuming quasi-static conditions...
...the lines and contours of A relate to B like the lines and contours of B relate to j.
Should this last j be a capital J?
:Yes and fixed. Constant314 (talk) 13:17, 18 May 2022 (UTC)
thread_title:  Capital vs small J in [[Magnetic_vector_potential#Depiction_of_the_A-field|Depiction of the A-field]] 

message: Since 
\nabla \times \mathbf{B} = \mu_0\mathbf{J}
assuming quasi-static conditions...
...the lines and contours of A relate to B like the lines and contours of B relate to j.
Should this last j be a capital J?
:Yes and fixed. Constant314 (talk) 13:17, 18 May 2022 (UTC)
thread_title:  Depiction of the A-field