Talk:Displacement current/Archive 2

From Wikipedia, the free encyclopedia

Archive This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Contents

'Displacement' current in radio transmission

A radio transmitter aerial and receiver aerial form a capacitor arrangement:

_______||__________

Catt is right at http://www.ivorcatt.com/2604.htm to point out that Maxwell ignored the flow of light speed energy along the plate connected to a charge. He is wrong to ignore my statement to him, based on Feynman's heuristic quantum mechanics and my fairly deep mechanistic knowledge of radio from experimenting with it myself instead of reading equations and theories from armchair experts in books (I read the books after experimenting, and found a lot of ignorance).

Radio transmitter aerial: |

Radio receiver aerial: |

Transmitter aerial and receiver aerial arranged for strong reception: ||

Transmitter aerial and receiver aerial arranged for zero reception: --

Transmitter and receiver aerial in a more usual situation (receiver picking up a much weaker than transmitted field): |….. |

Hence, a radio link is a capacitor, with radio waves the ‘displacement current’. This is the simplest theory which fits the experimental facts of radio! It was Prevost in 1792 who discovered that if a cooling object is also receiving energy in equilibrium, you don’t measure a temperature fall.

I dont understand the significance of the last statement about Prevost-- can you expand on it please?--Light current 01:01, 14 December 2005 (UTC)
And what, pray, would be the capacitance between the two aerials if spaced say 500 miles apart?. And what would be the capacitive reactance between the aerials? And therefore what loss would there be between the 2 aerials ? (in dB).--Light current 03:58, 29 December 2005 (UTC)

Maxwell’s 1873 Treatise on Electricity and Magnetism, Articles 822-3: ‘The ... action of magnetism on polarised light [discovered by Faraday not Maxwell] leads ... to the conclusion that in a medium ... is something belonging to the mathematical class as an angular velocity ... This ... cannot be that of any portion of the medium of sensible dimensions rotating as a whole. We must therefore conceive the rotation to be that of very small portions of the medium, each rotating on its own axis... The displacements of the medium, during the propagation of light, will produce a disturbance of the vortices ... We shall therefore assume that the variation of vortices caused by the displacement of the medium is subject to the same conditions which Helmholtz, in his great memoir on Vortex-motion, has shewn to regulate the variation of the vortices of a perfect fluid.’

‘… the source of the gravitational field can be taken to be a perfect fluid…. A fluid is a continuum that ‘flows’... A perfect fluid is defined as one in which all antislipping forces are zero, and the only force between neighboring fluid elements is pressure.’ – Bernard Schutz, ‘General Relativity’, Cambridge University Press, 1986, pp. 89-90.

Quantum field theory ?

Feynman noted that the drag effect of the spacetime fabric only works on the dv/dt not on v. So it is not like air. It only resists accelerations. The 'drag' is thus inertia, and causes the Lorentz-FitzGerald contraction. The reason why it doesn't continuously slow things down is that equilibrium re-establishes as a result of the Lorentz-FitzGerald contraction. Penrose has a diagram depicting the contraction of electric field strength in the direction of motion around a moving charge. This makes it clear how the equilibrium is restored, allowing motion: the charge distorts in shape when moving, so that the pressure on it from each direction remains equal, preventing continuous drag. The Feynman diagrams, part of the heuristic framework for making progress in QFT, create difficulties: the gauge bosons carrying the forces should be dealt with physically, if they really do create force. QFT is incomplete, and the pictorial Feynman diagrams are just treated as a calculating aid to identify and classify different types of calculation and interaction, not to show mechanisms for causality.

Please understand that the two curl equations are unified by the Heaviside vector E = cB, where E is electric field strength and B is magnetic field strength, and all three vectors E, c, and B are orthagonal, so the curl vector (difference in gradients in perpendicular directions) can be applied simply to this unique E=cB:

curl.E = c.curl.B

curl.B = (1/c).curl.E

Now, because any field gradient or difference between gradients (curl) is related to the rate of change of the field by the speed of motion of the field (eg, dB/dt = -c dB/dr, where t is time and r is distance), we can replace a curl by the product of the reciprocal of -c and the rate of field change:

curl.E = c [-(1/c)dB/dt] = -dB/dt (Faraday’s law of induction)

curl.B = (1/c) [-(1/c) dE/dt] = -(1/c2 ) dE/dt (‘displacement current’ ???)

Notice that all electrons have a magnetic field as well as an electric field, see for example: http://photos1.blogger.com/blogg...00/ electron.gif; a Heaviside energy vector trapped by gravitation is an electron (magnetic field dipole mechanism can be seen here: http://members.lycos.co.uk/nigelbryancook/Image11.jpg). The eternal magnetic fields of charges are normally cancelled out by the pairing of electrons with opposite spins (Pauli exclusion principle). From Nigel Cook, 13 Dec 05

From Mr Nigel Cook?

Please note the best version of the Catt 1978 article, which has the diagrams, is:

http://www.ivorcatt.org/icrwiworld78dec1.htm http://www.ivorcatt.org/icrwiworld78dec2.htm

Quantum field theory QFT is the mathematical unification of special relativity and quantum mechanics to deal with electron spin (which is circular motion, with acceleration that is not strictly a valid application of special relativity, which only deals with uniform, non-acceleration situations right). QFT contains difficulties like the need for renormalisation to limit the integral of interactions of the electron core and the polarised vacuum surrounding it. Some of these problems come from special relativity, which has only 2 postulates and is a flat earth theory, since the more complete theory is general relativity has 3 postulates, the last of which is basically interpreted as the existence of a spacetime fabric. I've analysed the atom as a capacitor using Catt's stuff in Electronics World, August 2002, and gravity using Catt's spacetime fabric and the big bang in Electronics World April 2003. Summaries of the material are on my site now at http://feynman137.tripod.com/ and blog http://electrogravity.blogspot.com/ . I've had long discussions with Catt at his home in St Albans, but he wants nothing to do with quantum field theory. Basically, he has been suppressed by mainstream journals and just wants to get his own back by calling them crackpots, which is backfires and makes him look eccentric/paranoid to the media.

http://cosmicvariance.com/2005/11/14/our-first-guest-blogger-lawrence-krauss/:

The whole basis of the energy-time version of the uncertainty principle is going to be causal (random interactions between the gauge boson radiation, which constitutes the spacetime fabric).

Heuristic explanations of the QFT are required to further the basic understanding of modern physics. For example, Heisenberg’s minimum uncertainty (based on impossible gamma ray microscope thought experiment): pd >= h/(2Pi), where p is uncertainty in momentum and d is uncertainty in distance. The product pd is physically equivalent to Et, where E is uncertainty in energy and t is uncertainty in time. Since, for light speed, d = ct, we obtain: d = hc/(2Pi.E). This is the formula the experts generally use to relate the range of the force, d, to the energy of the gauge boson, E. Notice that both d and E are really uncertainties in distance and energy, rather than real distance and energy, but the formula works for real distance and energy, because we are dealing with a definite ratio between the two. Hence for 80 GeV mass-energy W and Z intermediate vector bosons, the force range is on the order of 10^-17 m. Since the formula d = hc/(2.Pi.E) therefore works for d and E as realities, we can introduce work energy as E = Fd, which gives us the strong nuclear force law: F = hc/(2p d^2). This inverse-square law is 137 times Coulomb’s law of electromagnetism.

The heuristic explanation of this 137 anomaly is just the shielding factor by the polarised vacuum:

‘All charges are surrounded by clouds of virtual photons, which spend part of their existence dissociated into fermion-antifermion pairs. The virtual fermions with charges opposite to the bare charge will be, on average, closer to the bare charge than those virtual particles of like sign. Thus, at large distances, we observe a reduced bare charge due to this screening effect.’ – I. Levine, D. Koltick, et al., Physical Review Letters, v.78, 1997, no.3, p.424.

The muon is 1.5 units on this scale but this is heuristically explained by a coupling of the core (mass 1) with a virtual particle, just as the electron couples increasing its magnetic moment to about 1 + 1/(2.Pi.137). The mass increase of a muon is 1 + 1/2 because Pi is due to spin and the 137 shielding factor doesn’t apply to bare particles cores in proximity, as it is due to the polarised vacuum veil at longer ranges. This is why unification of forces is approached with higher energy interactions, which penetrate the veil.

This idea predicts that a particle core with n fundamental particles (n=1 for leptons, n = 2 for mesons, and obviously n=3 for baryons) coupling to N virtual vacuum particles (N is an integer) will have an associative inertial mass of Higgs bosons of:

(0.511 Mev).(137/2)n(N + 1) = 35n(N + 1) Mev, where 0.511 Mev is the electron mass. Thus we get everything from this one mass plus integers 1,2,3 etc, with a mechanism. We test this below against data for mass of muon and all ‘long-lived’ hadrons. ... more at http://feynman137.tripod.com/ ... best wishes. Nigel

Nigal said: "Quantum field theory QFT is the mathematical unification of special relativity and quantum mechanics to deal with electron spin...". Dirac dealt with SR and the spin of the electron with the Dirac equation. The development of Quantum field theory was required to deal with the creation and destruction of particles.
Nigal said: "Some of these problems come from special relativity, which has only 2 postulates and is a flat earth theory...". A Flat earth theory? Alfred Centauri 14:24, 26 November 2005 (UTC)

Flat earth assumptions would give physics laws useful for ants. Similarly, 2-postulate relativity works if there is no gravity to affect uniform motion. Since there is gravity, and space is thus curved, special relativity never strictly applies, except as an approximation in this real universe ('special' as called by cranks, 'restricted' as called after general relativity, which deals with accelerative motion, which the 1905 theory does not apply to). General relativity is entirely different in structure, and the mathematical results of restricted relativity are just approximations since in the real world accelerations are required both before and after any uniform motion occurs, and most supposedly uniform motion is actually accelerative (special relativity does not apply to the earth's rotation or the motion of the planets, which involve centripetal accelerations), see http://feynman137.tripod.com/

Nigel could you please sign/date your posts by typing four tildes. THis would help us all to keep track of things. THanks!--Light current 01:49, 7 December 2005 (UTC)

It is a common error to state that SR does not apply to accelerated motion. GR is a theory of gravity where gravitation is a manifestation of curved spacetime. In GR, acceleration is relative. However, accelerated motion in flat spacetime does not require GR - SR alone is adequate. Alfred Centauri 21:13, 6 December 2005 (UTC)

GR does not say acceleration is subject to the principle of relativity which is why Einstein had to introduce a third postulate (SR has only two postulates) that contradicts relativity for accelerative motion:

‘The special theory of relativity … does not extend to non-uniform motion … The laws of physics must be of such a nature that they apply to systems of reference in any kind of motion. Along this road we arrive at an extension of the postulate of relativity… The general laws of nature are to be expressed by equations which hold good for all systems of co-ordinates, that is, are co-variant with respect to any substitutions whatever (generally co-variant).’ – Albert Einstein, ‘The Foundation of the General Theory of Relativity’, Annalen der Physik, v49, 1916.

The principle you mean is I think that the effect of gravitational acceleration is equivalent to that of inertial acceleration. The maths is dealt with http://feynman137.tripod.com/ where it is proved SR by the equivalence principle gives the contraction term of GR. Special relativity is best obtained from general relativity as a limiting approximation for straight line motion, with the proviso that there is no straight line motion in reality, so it is really wrong. To teach special relativity to people as being correct is wrong, like teaching a flat earth theory without saying that in reality it does not apply except as an approximation for very limited uses. - Nigel Cook 12 Dec 05.


Later Developments

I suggest this section be removed, because (1) Ivor Catt is not in the mainstream, (2) what does that mean, doubting the existence of displacement current? As I keep saying, displacement current is just the time derivative of the electric field times epsilon! It can't not exist. Nobody says it's a real current (movement of charge). Anyone who says that displacement current does not exist is not wrong, but confused, and will confuse everyone else within earshot. Pfalstad 00:38, 23 December 2005 (UTC)

The alternative view which is now over 30 years old ought to be given! Pleas rewite in a clearer way but do not remove these references. We're here to list knowledge not to hide it.--Light current 00:40, 23 December 2005 (UTC)

Ok, you're probably right; enough people get all excited about displacement current that it's probably worth mentioning. I'm going to delete your link though. Surely you can find something better than that. For one thing, he could at least skim a physics textbook to realize that the "D" in "D = epsilon E" is not displacement current. Pfalstad 01:02, 23 December 2005 (UTC)

"A number of people such as Ivor Catt have stated that displacement current as defined above does not exist but that it is intimately bound up with the electromagnetic wave." I'm not sure you're accurately representing Catt's views. Of course I can't blame you because I can't understand what the hell he's talking about half the time. But when you say displacement current "as defined above" does not exist, I don't think that's right, because as I've defined it, it can't not exist. It's a derivative of a physical quantity; how can it not exist? And where does he say that it doesn't?

See here [1]--Light current 07:22, 23 December 2005 (UTC)

If we're going to claim that he said something that meaningless, we should quote him directly. And where does he say that it's intimately bound up with the electromagnetic wave?

Heres the one about the em energy rather than disp currrent [2]--Light current 07:33, 23 December 2005 (UTC)

Should we simply say that he has attacked the idea of displacement current and its role in electromagnetism, saying that it is unnecessary and misleading? Pfalstad 06:10, 23 December 2005 (UTC)

I read the first link, Displacement Current and how to get rid of it, and he says displacement current is a "mathematical manipulation". It makes no sense to say a mathematical manipulation does not exist. He says it is an artifact of a flawed model of a capacitor. He does not say it does not exist. He seems to be objecting to the identification of dE/dt as displacement current, and also thinks the traditional model of a capacitor (which emphasizes that) is flawed. He also says, in the second link, "It is not a coincidence that `displacement current' saves the idea of continuity of electric current; it does so by definition." So he seems to be attacking the terminology and the emphasis on displacement current, but does not say it does not exist, because that wouldn't make any sense. Pfalstad 20:37, 23 December 2005 (UTC)

After reading some of the recent changes that some anon dumped on the Ivor Catt article, it seems clear that Ivor Catt mostly objected to Maxwell's simplistic model of the capacitor, and that's why he keeps trashing displacement current, which came into existence to refine the capacitor model. Maxwell used displacement current to salvage Kirchoff's laws; the "current" caused by the changing electric field matched the real current in the wires leading to the plates. Maxwell thought it was a more-or-less steady current. So if the capacitor is treated as a transmission line (which it must be at high frequencies), then it's not a steady current, and talking about displacement current is inappropriate and unnecessary. Transmission line equations should be used instead. So Ivor Catt isn't a crank; he just needs a better editor, maybe. Pfalstad 01:56, 27 December 2005 (UTC)

Agreed--Light current 02:18, 27 December 2005 (UTC)

Great! Now, even though Maxwell's model of the capacitor wasn't perfect, the displacement current idea led to his discovery of Maxwell's equations (by making a necessary change to Ampere's law), and the electromagnetic wave equations. I don't think Catt is disputing those. Pfalstad 15:48, 27 December 2005 (UTC)

I think he is disputing disp current regardless of what Nigel says. If you read the displacement current article carefully the tone is one of disbelief and the introduction says its not needed!--Light current 20:24, 27 December 2005 (UTC)

You think he is disputing Maxwell's equations and the electrodynamic wave equations in their current form? I don't see any indication of that. If he didn't think they were correct, he would suggest an alternative form. The article says displacement current is not needed for the capacitor. Pfalstad 04:50, 28 December 2005 (UTC)

I think he is disputing disp current in capacitors (and by implication discrediting the idea generally) in the article Displacement current (and how to get rid of it)[3] He doesnt mention Maxwells equns here. I quote from the article p1 (top rhs):
The excision of displacement current from electromagnetic theory....

THis implies strongly to me that he believes that disp current is not needed in any part of em theory (not just capacitor theory)

--Light current 19:22, 28 December 2005 (UTC)

Right, but the whole article is about capacitors. I think we should stick to what he says and not try to guess what he is implying. It's hard enough to figure out what he's saying explicitly. Pfalstad 19:34, 28 December 2005 (UTC)

No. The article's about disp current. That's why its called displacement current. He's just using the capacitor/ TL as a (very good) example of the silliness of the idea of disp current.

Quote:

To enable the continuity of electric current to be retained across a capacitor Maxwell proposed a "displacement current". By treating the capacitor as a special kind of transmission line this mathematical convenience is no longer required.

my bolding --Light current 19:43, 28 December 2005 (UTC)

Right, OK, you're right, we'll just report what he says and not try to make sense out of it. Pfalstad 15:09, 29 December 2005 (UTC)

You know it makes sense (or not as the case maybe)--Light current 18:41, 29 December 2005 (UTC)

Controversies

Can I stick my oar in and suggest that this section might be better titled "Controversies", or something similar? There are several represented directly on this discussion page.

To start with, Maxwell's choice of the name "displacement current" is a problem, particularly since he was thinking of an "ether", which has since been rejected by "mainstream physics", but which still has adherents (some of whom are professors of physics!) Furthermore, Einstein derived Special Relativity directly from Maxwell's Equations (and the derivation of the speed of light in particular) and, of course, there are still "relativity deniers" out there.

I suspect that Catt had/has problems understanding the concept of "electron drift" as the explanation of current flow. There is certainly a reference in his writing that suggests this, and Nigel Cook, who echos a lot of Catt's ideas, has repeatedly tried to prove that current flow is due to a "TEM wave" by asserting that the kinetic energy of the conduction electron mass moving at the electron drift velocity is far too small. It's hard to tell which came first, but I'm pretty sure that the "correct" description of displacement current is inimical to Catt's TEM waves. In the 1980's Catt produced several articles trying to break the mathematics of Maxwell's Equations. This one Maxwell's Equations Revisited from 1980 establishes Catt's level of competence in calculus. He was still linking to it in 2004 The new Scholsticism - (Follow the link to "theory of flight" and try to read the last paragraph without laughing....)

Returning to this page... relegate Catt to the end of the section as a "notable recent doubter" - the current placing really over-states his relevance. -- Kevin Brunt 21:26, 5 January 2006 (UTC)

You are free to move things, Kevin. No one owns this page. Be our guest!.--Light current 00:41, 6 January 2006 (UTC)
I just read some of Catt's articles, and it seems to me the entire crux of his argument is that the behavior of real capacitors is more complex than the ideal capacitor model that is used in analyzing circuits consisting of lumped elements. To me, that is kind of like saying that Newton's laws of motion are incorrect in light of special relativity. That is true, but if you are trying to analyze the trajectory of a baseball as it leaves the bat and sails over the Green Monster, it is generally fine to use Newton's laws instead of relativity. Technically, Newton's laws give the wrong answer, but at the very low speeds involved, the difference is so incredibly small that it is more than insignificant. Catt's arguments only apply at very high frequencies or for capacitors of very large physical dimensions. -- Metacomet 05:11, 6 January 2006 (UTC)
Yes , I agree.--Light current 23:06, 6 January 2006 (UTC)

[Responding to Metacomet...] Catt is an "engineer". I think that in his undergraduate days, Engineering was rather looked down upon by Science and particularly in Cambridge (which only started accepting women students in the late 1940s) Science and Engineering were still regarded as infra dig by "proper academics". Catt has a definite chip on his shoulder about pure science, and grossly undervalues subject areas outside his blinkered viewpoint. For instance, he clearly thinks that the difficult part of building a computer is still the hardware, rather than the software. -- Kevin Brunt 21:25, 9 January 2006 (UTC)

Furthermore, even if you accept his argument, which is to say that if you treat the capacitor as a transmission line, which is driven by wires connected to the center of the plates with EM waves that propagate outward to the edges of the plates, don't you still need the displacement current to explain what happens to the real current once it reaches the edge? In other words, hasn't he simply moved the problem from the center of the plates to the edge of the plates? Once the current reaches the edge of the top plate, how does it get to the bottom plate? Wouldn't you have to say that it is Maxwell's displacement current that allows the current to flow form the edge of the top plate to the edge of the bottom plate? -- Metacomet 05:18, 6 January 2006 (UTC)
In my opinion, no . If you treat the problem as one of em enrgy travelling from center to periphery then reflecting, no transverse current is required!.--Light current 23:12, 6 January 2006 (UTC)

As I noted below, Catt, Davidson and Walton appear not to understand that the equations for the transmission line are derived by dividing it up into short sections, each with its own bit of inductance, capacitance and resistance, and doing the "in the limit as length -> 0" trick to get a pair of differential equations. This approach avoids the high frequency/large size issues by allowing each point on the line to have its own individual properties. Rather than abolishing displacement current, it is now distributed all down the transmission line. Catt's more recent letters in Electronics World have claimed that he has shown that the energy cannot "cross the gap" until it has reached the "end" of the capacitor, which is at odds with the multiple capacitor model. -- Kevin Brunt 21:25, 9 January 2006 (UTC)

I think the problem starts about here. Catt et al Dgtl Hrdwre Dsgn pg10 Catt and his collaborators seen to think that the derivation of the Telegrapher's Equations from first principles yields a prediction of a "spurious high-frequency cutoff" - in fact this cutoff is due to the inclusion of the resistance of the conductor and the conductance of the dielectric, which Catt et al ignore. I suspect that they think that the "spurious cutoff" is theory diverging from reality rather than the converse. Certainly, they don't appreciate that the reason why they can model a capacitor as a transmission line is because a transmission line is a capacitor (or rather a whole series of capacitors) in the first place. The "distributed model" is merely a way of modelling the way that the charge spreads across the capacitor. I would imagine that if you did the integration over a surface that properly divided the two conductors of the transmission line you would come up with exactly the same numbers as you would for a "point" capacitor. (Yes, you would have to allow for the "step" nature of the current flow, but a 1-dimensional "Catt" capacitor is just as arbitrary as a 0-dimensional "point" capacitor.) -- Kevin Brunt 16:22, 6 January 2006 (UTC)

By the way, it is possible to construct an argument regarding inductors that is virtually identical to Catt's argument with respect to capacitors, and in so doing, demonstrate that the B field is completely unnecessary. After all, an inductor is really just a short circuit, so how indeed is it possible for an inductor to support a voltage across its terminals? In fact, couldn't you simply argue that an inductor is nothing more than a transmission line (think of a hollow cylindrical tube of highly conductive metal with a conductor attached at each end)? So maybe we should simply dispense with the time rate of change of the magnetic flux density... -- Metacomet 05:29, 6 January 2006 (UTC)
An inductor is a transmission line according to Catt et al. If that means you dispense with dB/dt, then so be it!--Light current 02:45, 10 January 2006 (UTC)

Prize challenge

Experiment to measure displacement current in a parallel plate disc capacitor, or a transmission line equivalent

I would be interested to know if any one has any ideas on how to measure displacement current in an air spaced capacitor. My only stipulation is that the procedure must not use the measuremrent of any magnetic field to infer the displacement current.

This is because Im trying to prove that there is no current, not that there is no magnetic field. The presence of magnetic field will not be taken as evidence of displacement current. Suggestions welcomed here!--Light current 02:19, 25 December 2005 (UTC)

Just an additional note about vacuum capacitors. Obviously, any so called 'displacement current' will be equal in magnitude to the conduction current in the leads, so it should be easy to measure one would think! If its not easy to measure or it can only be measured as changing electric filed, magnetic filed, flux density or some other derived quantity, then perhaps disp current is an erroneous concept and real curernt does not actaully pass from one plate to another. But then you get the problem of how the external conduction current gets from one plate to the other!!--Light current 17:42, 12 January 2006 (UTC)

I don't think you're going to get anyone taking this up. The term "displacement current" ia an anomaly resulting from Maxwell's attempt to explain electromagnetism in terms of a fluid "aether". The aether concept was eventually abandoned because it created more problems than it solved, but Maxwell's terminology lives on as a convenient and universally-recognised label for the principle that a changing electric field creates an magnetic field.

Kevin Brunt.

Dont you mean creates a magnetic field here?--Light current 11:26, 12 January 2006 (UTC)

Yes! (Fixed) -- Kevin Brunt 15:45, 12 January 2006 (UTC)
The name is a historical oddity; much like the proto-whale that has been saddled with the name Basilosaurus (meaning "King Lizard") because the chap who dug up the first fossil was hoping it was a dinosaur.
Many modern physicists would like to ditch the name precisely because there is no "flow" of the sort that Maxwell postulated. However, if they do so they would find it that much harder to deal with calls to deal with the "mistake" over conventional current as well. And of course there are theories that explain fields and forces in terms of the flow of "virtual particles" - but that remains speculative. -- Kevin Brunt 21:02, 10 January 2006 (UTC)

Kevin I find myself agreeing with you, but there are still people out there who believe DC is a real current flowing from one plate of a capacitor to the other. In fact I thought you believed it!--Light current 22:48, 10 January 2006 (UTC)

Like who? Pfalstad 22:56, 10 January 2006 (UTC)

Not you!--Light current 22:58, 10 January 2006 (UTC)

What's this now? You want to see if there's a way to measure a changing electric field in a capacitor? Pfalstad 21:15, 10 January 2006 (UTC)

Paul Are you actually seriously implying that the two quantities are exactly the same and that one cannot be differentiated from the other?? --Light current 19:33, 11 January 2006 (UTC)

Please dont tease Paul! NO. I want to know how to measure actual curent flowing betwen plates in an air or vacuum capacitor.Ie current as you would measure with an ammeter. This challenge is not open to User:Pfalstad as it appears he does not admit the existence of actual flow of real current and so does not need to be convinced.--Light current 22:45, 10 January 2006 (UTC)

I ask who because, rather than guess what the form the current might take, it seems easier to just go find these people, find out what they think displacement current is, and then show that they are wrong. Pfalstad 01:25, 12 January 2006 (UTC)

I am in the process of doing just that. I have foud out what you believe DC to be. Im in the process of finding out what Alfred Centauri believes it to be.--Light current 04:20, 12 January 2006 (UTC)

LC, please define what you mean by a 'real current'. By real, do you mean electric charge? Or, do you mean a flow of something real (physical) but not necessarily electric charge? Alfred Centauri 23:53, 10 January 2006 (UTC)

No I don't mean electric charge necessarily (I think we all agree that charges cannot generally flow thro' a vacuum). Lets define what I mean as a flow of 'something' that will produce a pd across a (small) resistance of infinitesimal thickness. Am I putting my neck in a noose here?--Light current 00:13, 11 January 2006 (UTC)

I'll assume you misspoke in your first sentence since we certainly don't agree that electric charge cannot flow through a vacuum (think vacuum tube). Regarding your definition of a real current: isn't resistance defined in terms of electric current? BTW, I'm not looking to set a trap. My question was honest - I think that many arguments (discussions?) here are due to a lack of agreement on terms. I need to know what you mean by 'real current'. FYI, I think of 'real current' as the flow of something where that something is a measureable quantity. Thus, the question of whether or not displacement current is a real current technically depends on whether electric displacement is a physically measureable quantity. Alfred Centauri 02:11, 11 January 2006 (UTC)

I did not 'missspeak' because I included the qualifier 'generally' as I knew you would pick me up on thermionic or vacuum emission etc.

I agree wholeheartedly that many arguments are caused by lack of agreeement (or confusion) on terminology. I think someone famous once quoted a saying on this very subject! I have just realised a mistake I made in my definition (which you have not commented upon). That mistake is that a resistor of infinitesimal thickness must necessarily have zero resistance.

So, to define current (or flow of something) I think your defn as 'something: where that something is a measureable quantity' + 'seen to be traversing from one point to another' is reasonable as a start. Remember tho' that I will not allow magnetic field measurements to be taken as evidence of current flow!. Also remember that we are dealing with a vacuum or air spaced capacitor where no displacement of charges can be detected.(ie I dont allow methods that depend on measuring charge displacement-- just to make things difficult!)--Light current 02:29, 11 January 2006 (UTC)

So, once again we need to clarify terms specifically, what is meant by electric displacement. Formally, displacement current is the flow of electric displacement. What is electric displacement? In your last sentence, you use the phrase 'charge displacement'. I suppose here you are referring to changes in the arrangement of the dipoles within a dielectric. Is this what you think of as electric displacement? Alfred Centauri 14:07, 11 January 2006 (UTC)

Ah here we have a disagreement in terminology. I was always led to believe that 'displacement' current was a flow of something due to the displacement of bound charges as you get in dielectric. So in my defn, 'displacement' is an adjective and not a noun. I am only familiar with defn like D =epsilon E and D in this case is the electric flux. So the current you get in a dielectric is easily seen to be due to the temporary displacement of the bound charges. I have no problem with this.

However, in a vacuum, there are obviously no charges of any sort present and therefore nothing physical can be 'displaced'. THe definition of 'displacement current' then needs to be modified, you seem to be saying, into one where it is a flow of this esoteric entity called 'displacement'. How do you define 'displacement' in this scenario? is it D (=E epsilon)?--Light current 18:14, 11 January 2006 (UTC)

I am not convinced that it is at all helpful trying to think in terms of displacement current "flowing". At the "level" at which Maxwell's equations apply there is "charge" which is inside the conductors and there is "electric field" which is somehow caused by charge and which is between the conductors. Neither of these concepts is explained at this level; they just "are".

If charge resides in the 'conductors', where does it reside in the electromagnatic wave in vacuo?--Light current 04:46, 12 January 2006 (UTC)

Maxwell was looking to his "aether" as a way to explain the phenomena; instead we now have merely shifted the goalposts by defining charge as a property of electrons and protons. The electric field is something that transmit forces between the charged particles; a dielectric "amplifies" the field because its charges move away from their equilibrium position in a direction that reinforces the field. -- Kevin Brunt 23:51, 11 January 2006 (UTC)

Well this last post reinforces my argument in that, if nothing actually flows, there is no current and Im happy with the idea. However, the term 'current' does imply flow of something. So perhaps the concept is misnamed?--Light current 04:12, 12 January 2006 (UTC)