Talk:Displacement current density

Expert Attention Necessary

I just added the flag:

to the top of the article. This is a really, really bad article in its current state. A brief skim of the commentary below tells me it has largely been authored by individuals who know little or nothing about the topic - a typical cut and paste from elsewhere wikipedia approach.

The phrase 'Displacement Current' is an unfortunate historical legacy. It really has nothing to do with capacitance - the displacement current is the only cross coupling mechanism in the homogeneous Maxwell equations, where there simply is no charge of any kind. Those are the equations governing radiation, which unequivocally empirically exists, and is now a foundational component of our technological infrastructure.

A good beginning would be to address units in the introduction or a first section. Currently, units are not addressed at all. Regarding units, the electric field E is related to the magnetic coercive force H just as the displacement current D is to the magnetic flux density B. When you get that clearly expressed, the rest of the garbage in the article will rapidly disappear. There is no magnetic charge whose SI unit is the Weber. There is electric charge, whose SI unit is the Coulomb. Just as the fact that the Weber appears as a unit in magnetic descriptions does not imply the existence of the charge, the appearance of the Coulomb in electric descriptions does not imply the necessity of electric charges. If anything, the presence of actual electric charges in some situations is the anomoly, not the displacement current.206.116.24.195

The article can certainly use some improvement, but on the issue of units, it is clear: displacement current has the same units as conduction current. In fact, that the reason displacement is called a current is because it has the same dimensions as current and simply adds its effects to the effects of conduction current.

Some things that I would like to see in the intro include the fact that the differential terms in Maxwell’s equation’s are displacement current densities (which have the same units as current densities). I would also like for it to be pointed out that there are two displacement current densities in Maxwell’s equations: the electric displacement current (dD/dt) and the magnetic displacement current (dB/dt). It is interesting that the electric displacement current is seen as something mysterious that requires a lot of explanation and analogies whereas the magnetic displacement current is simply accepted has a fact. Constant314 (talk) 00:42, 22 January 2018 (UTC)

@Constant314: I agree that it should be described as displacement current "density". On your other point, I feel that calling the analogous term ($d\mathbf {B} /dt$) in Faraday's equation "magnetic displacement current" (if that's what you were suggesting) would be very confusing for readers. This already has a name, electromagnetic induction. I wouldn't mind adding mention in the article that electromagnetic induction is the magnetic analogue (dual) of displacement current. BTW, I think the reason displacement current is seen as "mysterious" is due to the asymmetry of sources. The main source of $\mathbf {curl\,B}$ is the current density $\mathbf {J}$, and this overshadowed displacement current for a long time. In contrast, rate of change of flux $d\mathbf {B} /dt$ (electromagnetic induction) is the only source of $\mathbf {curl\,E}$, so it was discovered earlier, in 1831. If magnetic monopoles existed, a current of monopoles would create a solenoidal (circular) electric field around it, there would be a source term $\mathbf {J_{M}}$ on the righthand side of Ampere's equation, and electromagnetic induction would also be a minor effect; "something mysterious that requires a lot of explanation".

@206.116.24.195: I am not clear on what "garbage" you would like to remove from the article. I would like to see a little less description of displacement current as a "current", since it is not one, but Constant314 has already removed most of that amateur stuff from the article. --Chetvorno^TALK 02:53, 22 January 2018 (UTC)

@Chetvorno: Thanks for the kind words. There are good references referring to dB/dt as magnetic displacement current (Balanis, Harrington, Jordan & Balmain). In the interest of accuray, there are two terms called displacement current. It would be sufficient to note that this article is about the electric displacement current without dwelling on the other.Constant314 (talk) 03:20, 22 January 2018 (UTC)

On second thought, an about box would take care of it.Constant314 (talk) 03:58, 22 January 2018 (UTC)

I have addressed some of the issues and there have been no further comments for about 14 months, so I am going to remove the expert needed box. If anyone wants to restore the box, please add a new reason or start a new talk topic. Constant314 (talk) 23:30, 9 March 2019 (UTC)

One thing that is seriously wrong is the diagram with the text 'Example showing two surfaces S1 and S2 that share the same bounding contour ∂S.' In that diagram, S1 and S2 do not share the same bounding contour (thanks to Ivor Catt for pointing this out)! --Brian Josephson (talk) 20:59, 27 July 2020 (UTC)

What I pointed out was different; http://www.ivorcatt.org/icrwiworld78dec1.htm . The current entering the capacitor flows sideways along the capacitor plate. Maxwell and Heaviside failed to notice this. Ivor Catt. 30 July 2020 — Preceding unsigned comment added by 2.24.141.99 (talk) 20:24, 30 July 2020 (UTC)

I'm very aware that you think that, but I very much doubt if that is the case.--Brian Josephson (talk) 20:30, 30 July 2020 (UTC)

It looks to me like they do share the same bounding contour. Maybe I am missing something. Perhaps it is not obvious that S2 is closed underneath the capacitor plate. Constant314 (talk) 21:02, 27 July 2020 (UTC)

I see what you mean, it is more that it is unclear what S2 is. If the label S2 were put to the right of the picture (and then perhaps partial-S moved to the left for clarity) then that would improve things. I see that the person who drew the diagram (Chetvorno) is taking part in this discussion so perhaps he can adjust the diagram for us? --Brian Josephson (talk) 21:11, 27 July 2020 (UTC)

And maybe a closed ellipse for the base would help a bit also — I don't know. --Brian Josephson (talk) 21:16, 27 July 2020 (UTC)

I tweaked the caption. Constant314 (talk) 21:18, 27 July 2020 (UTC)

Good, I guess that helps. Though it might be argued that the whole explanation is far too lengthy!--Brian Josephson (talk) 10:46, 28 July 2020 (UTC)

Electric displacement field

Please see Talk:Electric_displacement_field#Delete,_and_change_to_a_redirect. fgnievinski (talk) 02:50, 27 August 2023 (UTC)

Maxwell's True Current

In Maxwell's Treatise, "True Current" is defined in vivid language and its importance is shown in examples.

"“One of the chief peculiarities of this treatise is the doctrine which it asserts, that the true electric current, that on which the electromagnetic phenomena depend, is not the same thing as the current of conduction, but that the time- variation of the electric displacement, must be considered in estimating the total movement of electricity, so that we must write, [the sum] .... as an equation of true currents.”

The text is from Vol. 2, Section 610, p. 232. I use the Dover edition.

The use of true or total current leads to an immediate proof of the divergence free solenoidal property of the right hand side of the Maxwell Ampere law. True current then has properties as universal and exact as the Maxwell equations themselves.

Should this quotation and some version of this discussion be in the article? Beisenbe (talk) 09:37, 14 July 2025 (UTC)

In my opinion, the section History and interpretation needs to be rewritten based on the literature on the history of science. That would include discussion Maxwell's conception of electric current and comparison to the modern concept based on the movement of electrons. For example, Jed Buchwald (1985) From Maxwell to microphysics . The quotation might be part of that discussion, but I don't think it should be included without discussing its context. Jähmefyysikko (talk) 10:26, 14 July 2025 (UTC)

The advantage of including the idea of true current is that it leads to new insights, not just history

True current is a field that has no divergence (in which the Maxwell equations are valid).

That means that true current does not accumulate on any known time scale.

and (here is new physics #1) true current must be the same in a series of chemical reactions.

That is a requirement on chemical reaction theory that is not in present day theories.

New physics #2

True current does not accumulate even during thermal motion. That means that in a one dimensional system (like a resistor or other circuit element) there is ZERO spatial variation of noise, even though there can be profound temporal variation of noise.

This fact is not included in theories.

In the treatment of two systems this is very important.

The flow of total current in one dimensional circuit components (used in every circuit in our computers) is altered by this consideration.

The understanding of how ion channel proteins (found throughout biological systems) is profoundly changed. Beisenbe (talk) 14:25, 14 July 2025 (UTC)

Quantum Scale Displacement Current

Displacement current is very important in the circuits of our computers that operate so quickly and are so small that quantum effects must be included in their design.

Given the technological and economic importance of computer circuits (that have determined much of our economic growth in the last decades), should not the article discuss the role of displacement current on the quantum scale? Beisenbe (talk) 14:30, 14 July 2025 (UTC)

The paper you cited (Ferry, Oriols and Robert Eisenberg 2025) justifies the need for the inclusion of displacement currents in quantum transport by citing more papers by Ferry and Oriols. Could you instead provide a textbook reference which discusses this? That would be much better indication that the topic is considered important. Jähmefyysikko (talk) 15:58, 14 July 2025 (UTC)