Talk:Ivor Catt/Archive 9

message: Would either (both) of you care to define exactly what you each mean by the term 'displacement current' (in vacuo). 
Q1 Is it for instance: 
* a) a flow of electric 'displacement' as User:Alfred Centauri would have it?
* b) dD/dt ( which may be the same as above)?
* c) electromagnetic radiation?
* d) nothing at all (ie doesnt exist)?
* e) something else? if so, what?
Q2 In which direction does it flow if it exists?
* a) from one plate of a parallel plate capacitor to the other plate (orthogonal to the plates) via the dielectric( eg air/vacuum)
* b) parallel to and between the plates
* c) in some other direction. If so - what direction?
I feel that a lot of the preceding disagreement may be due to lack of clarity in your definitions and explanations. Once you have both answered all the above questions, I think the discussion can be focused on any remaining disagreements you may have.--Light current 05:32, 24 February 2006 (UTC)
thread_title:  The fundamental questions 

message: Just so we all know who's saying what, I suggest we all follow these simple rules:
*Only reply outside the body of someone else's post. (ie dont interject in the middle)
*Sign and date all posts.
*Try to keep your horizontal tab space under each new heading (makes it much easier to follow one persons thread/ find his earlier posts etc).
*Keep all posts short and to the point (if possible).
*Try to introduce new headings if you are making a different point from the previous post(s). This makes it much easier to see what the hell were all discussing!
Thanks!--Light current 18:54, 24 February 2006 (UTC)
thread_title:  Rules of battle 

message: :LC, I'd start somewhat further back. Consider an arbitrary (passive) electronic component - a blob with two wires sticking out of it. It could be a capacitor, an inductor or a resistor. (It could even be a piece of wire disguised as a zero-ohm resistor for use with automated PCB machines.) Kirchoff's Current Law says that the current flow into the component is equal to the current flow out on the other side. This, of course, is only strictly true at DC, because it takes time for a change in the input current to be reflected at the output. This means during the time that the change takes to propagate through, there is an accumulation of charge. Furthermore, because there is an electric field associated with the charge, an increase (or decrease) in charge causes a change in the field What Maxwell did was to assert that there was a precise relationship between the difference in the "input" and "output" currents and the change in the field. Because he was considering the difference between two fields, he named the "extra term" derived from the changing field as a "current" as well. And because he was trying to interpret the phenomenon in terms of his "Aether" theory, with the changing field representing a "displacement" of the Aether itself, he came up with the label "displacement current". Many modern physicists would have been much happier if Maxwell chosen a name that was not so firmly tied into unconfirmed (and speculative) work. -- Kevin Brunt 15:39, 24 February 2006 (UTC)
replies: text: Thus, "displacement current" really means "there is a changing electric field here". I would tend to go with answer b) to Q1 (but wih reservations). Answer a) is probably putting too much "meaning" in. Answer c) has serious problems about the distinction between what displacement is, and what it causes. Answer d) is wrong, because there is a changing magnetic (I meant electric!) field. Answer e) has at least some truth in it. -- Kevin Brunt 15:39, 24 February 2006 (UTC)

text: As for Q2; firstly there is an issue with the "flow" - it assumes that the changing electric field is actually moving something, which moves the debate unnecessarily into the realms of quantum mechanics, etc, etc. For the purpose of understanding electromagnetism, it is only necessary to know that the field "is". As for the direction it acts in - it exists in 3D around the charge, so it operates in all directions. However, it interacts with its environment, so Q2 can really only be answered in the context of a specific situation. -- Kevin Brunt 16:00, 24 February 2006 (UTC)

text: Note that the argument in  "Displacement Current - and how to get rid of it" is based on the unstated (and incorrect) assumption that the concept of "continuity" underpinning Maxwell's derivation of "displacement current" is merely equivalent to Kirchoff's Current Law. Hence Catt (and presumably et al) believe that just by demonstrating that the charge does not "spread across the plates" instantly that they can break Maxwell's theory. The assumption, and the corollary, are false. -- Kevin Brunt 16:00, 24 February 2006 (UTC)

text: The "standard definition" of current is that it is motion of charge. Kirchoff's Current Law effectively assumes that charge moves infinitely fast, so that charge passing from the positive pole of the battery to the negative appears to pass through everywhere in the circuit simulataneously. The Telegrapher's Equations show that charge actually moves at a finite, but large, velocity that is affected by the properties of the circuit. The Drude Model and Quantum Mechanics, etc, show that the apparent motion of charge at near light speeds in an "empty" conductor is a sort of "summary" of the motion of a very large number of negatively charged electrons packed into a far-from-empty conductor. (An analogy could be drawn with the "Mexican Wave". -- Kevin Brunt 20:04, 25 February 2006 (UTC)

text: The upshot of all this is that a change in the current at one end of a conductor is not immediately "seen" at the other  end, and until that happens the flow of current out does not match the flow in, so that the total amount of charge in the conductor must be changing more or less by definition. This can be clearly seen in the case of a transmission line which has been properly terminated at both ends. It should be obvious that a change in the magnitude of the current at the source end of the line necessarily requires a change in the voltage there and that this voltage change propagates to the other end, where it will cause the current flowing in the terminating resistance to change. If you calculate the change of charge as the difference in the current times the propagation time you will find that it is tha same as the change in the voltage times the capacitance of the line. -- Kevin Brunt 20:04, 25 February 2006 (UTC)

text: "Accumulation of charge" is thus a consequence of the finite speed of motion of charge. -- Kevin Brunt 20:11, 25 February 2006 (UTC)

text: However, we are talking, in the main part, about the application of a DC voltage step to a TL. When we start looking at higher frequencies other effects come into play. It is part of the muddle that Catt created, and which Nigel is making worse, that these "other effect" have been dragged in too soon. At high enough frequencies the energy flow ceases to be a current flow in the conductor, and instead becomes an electromagnetic wave outside the conductor. Catt's "Theory C" cannot explain this observed transition. -- Kevin Brunt 19:47, 26 February 2006 (UTC)
thread_title:  Kevins position 

message: Since Maxwell was apparently unaware of em radiation he had to find a fix for Kichoffs laws. It is now agreed of course that Kirchoffs laws are but an approximation to the real happenings and that field theory tells the complete story in circuit analysis. In regard to your reply, Im happy to accept your defn (dD/dt) of displacement in vacuo. 
Im going to try to avoid use of the term current as this implies  a flow of something.--Light current 18:30, 24 February 2006 (UTC)
thread_title:  Comments on Kevins position by LC 

message: Light Current: Maxwell has all sorts of mechanical "displacement current" theories of the aether, but the facts are resolved by quantum field theory, which is experimentally confirmed.  If you charge up one plate, the other charges by induction, which means energy flows across to it as determined by quantum field theory (which should be considered the underlying mechanism for Maxwell's equations, and is more general).  
So 
*Q1: (c) electromagnetic radiation.  
*Q2: (a) orthagonal to the plates.  
The TEM wave is not however the mere charging of one conductor, but the charging of one conductor with positive charge and the charging of the other one with an equal amount of negative charge.  This is a very special situation, which allows a propagating wave to go, because each conductor is then sending an equal amount of displacement current energy to the other.  Nigel 172.212.141.83 16:34, 24 February 2006 (UTC)
thread_title:  Nigels stated position 

message: OK Nigel. Thanks for making your position clear. This is what I thought you were saying. But best to make sure. Ive just spaced out your post to make these answer easy to see. --Light current 18:54, 24 February 2006 (UTC)
replies: text: LC, the next thing we need to sort out is "TEM". Maxwell used the term "transverse electromagnetic wave" to refer to a very specific situation, following on from his extension of Ampere's equation, to predict that "displacement current" would create a magnetic field. Maxwell saw that when the J term was zero (ie no movement of charge) the equations interrelating the electric and magnetic effects reduced to a form suspiciously close to something that he already had solutions for. The solution he came up with has the electric and magnetic fields varying sinusoidally in directions at 90 degrees to each other, while moving in a direction perpendicular to both at a velocity dictated by the (observed) physical constants relating to the magnetic and physical properties. Furthermore, this velocity was sufficiently close to the measured velocity of light that Maxwell was legitimately able to speculate that light was an electromagnetic phenomenon. -- Kevin Brunt 22:25, 24 February 2006 (UTC)

text: The important point is that while there are any number of solutions to Maxwell's Equations, the term "transverse electromagnetic" is used by physicists exclusively to refer to this specific category of solution identified by Maxwell. Catt insists that his voltage step/Heaviside energy slab travelling down a conductor is "TEM", but while it is certainly "electromagnetic", it is simply not "transverse electromagnetic" within the standard definition used by physicists. In other words, "TEM" in Catt's "Theory C" does not mean the same thing as in "Theory N" as used by everyone else, and this is really what causes the Catt Anomaly. The "same songbook" that Catt thinks that all the physicists are singing out of is, in fact, a technical dictionary. -- Kevin Brunt 22:25, 24 February 2006 (UTC)

text: We need Nigel to clarify exactly what the "TEM wave" he just referred to is. -- Kevin Brunt 22:25, 24 February 2006 (UTC)
thread_title:  Comments on Nigels position  

message: Under review!
* electrons drift in an electric field
* displacement current only exists in dielectrics- it cant exist in vacuo.
* dD/dt exists -- so what?
* a magnetic field may exist that implies a normal current between capacitor plates etc but:
* nothing at all flows between the plates of capacitor normal to their surface (esp not energy).
* energy current flows parallel to and between the plates of a capacitor.
* capacitors and TLs charge up by extracting energy from the incident em waves and converting it to charge.
* therefore charge must be carried by em radiation somehow.
--Light current 22:30, 26 February 2006 (UTC)
thread_title:  LC's position 

message: It is well known that a TL can be charged fully from a matched source in the time it takes a step to travel to the far end and back to the source. Its used all the time for pulse charging of lines in radar pulsers etc, and can easily be demonstrated with a piece of coax, a fast switch and a fast scope.
In the case of short lines there is not sufficient time for charged particles to move along the line and take up their new static positions. So, where does this new static charge come form so quickly if not from the em energy fed into the line? (I hope this is not a rephrasing of the Catt Anomaly)--Light current 21:36, 26 February 2006 (UTC)
replies: text: LC. Yes, this is very closely related to the Catt Anomaly. I'm pretty certain that the question is lurking somewhere behind Catt's writings. It is explicit in Lynch's reformulation and Nigel, following on from Lynch, has tried to prove "Theory C" by showing that the kinetic energy of the electrons in motion in the conductor is insufficient to convey the energy associated with the current flow. Nigel's "proof" actually creates an entirely false picture - his model of "Theory N" has current without voltage, and his model of "Theory C" has voltage without current. A model that matches the observed facts needs to be able to accomodate current and voltage simultaneously; since Catt denies the existence of current, his theory has major difficulties at the outset. -- Kevin Brunt 13:22, 27 February 2006 (UTC)
replies: text: Kevin, Catt and I show that most (nearly 100%) of the energy transfer in electricity is energy of "radiation" or "electromagnetic field" (I dare not use weird "gauge boson" term to be concise, since someone here disapproves of QFT as being "weird"), not electron drift current.  Catt stated this in an article in WW in Sept. 84, Fundamentals of Electromagnetic Energy Transfer, around the time it was renamed "Electronics and Wireless World" ("and Wireless" was later dropped).  Catt thought this meant he could drop electrons altogether, so I took him a beta radiation emitter and a geiger counter, and asked him to explain the electrons.  He says trapped energy creates the illusion of "static" charge in charged capacitors and transmission lines, so if energy can be trapped into a small unit, you get an electron.  This agrees with the Standard Model of physics, which says electrons have no mass, and only obtain the illustion of mass by associating with a vacuum field that creates the inertial and gravitational effects of mass (Higgs field).  But despite this, Catt won't correct his material to include this, clinging on to a falsely simplistic picture which ignores electron drift altogether, which is wrong.  This is why I wrote about it in the August 02, April 03, and March 05 Electronics World.  However, Catt does nothing.  Nigel 172.201.86.143 11:42, 1 March 2006 (UTC)

text: To understand what is going on you need to start by carefully distinguishing between the 19th century description of electricity, in terms of "abstract charge", and the 20th century version, which explains the motion of abstract charge in terms of the underlying motion of charged particles (either sub-atomic particles or charged molecules, etc). Abstract charge moves in an "empty" conductor; it enters the conductor at one end, travels through it at exactly the right speed to match the observed behaviour, and leaves at the other end. On the other hand, electrons move in a conductor that is stuffed full of electrons, with the right number of protons to balance the charge; you push electrons in at one end, all the conduction electrons move down the conductor, and the same number of electrons leave at the other end. In the case of a capacitor, the electrons can leave, so the electrons in the conductor "squeeze up" to make room; there is then an excess of negative charge in the conductor, which is detectable outside it. The motion of the electrons is related to the notion of current; the push (which is a force) is likewise related to voltage. (Reverse directions as necessary for a positive applied voltage.) -- Kevin Brunt 13:37, 27 February 2006 (UTC)
replies: text: Kevin what you say is right for the steady state case, the part of the TEM wave where the voltage is constant, but not for the front electron where the voltage step is rising.  Whenever charge accelerates, it emits electromagnetic radiation transversely, and this happens in the rise portion of the front of the TEM wave.  Where the voltage is steady at 10 volts, the electrons can be treated as drifting at a steady pace (electron and atom interactions give rise to resistance hence energu loss as heat unless it is a superconductor).  Nigel 172.201.86.143 11:42, 1 March 2006 (UTC)

text: Arnold Lynch and Nigel are unable to get a "Newtonian mechanical" description of the motion of the electrons and the forces acting on them to come out correctly. I suspect that they are both trying to have the electrons move smoothly at the "electron drift velocity"; the explanation of resistance as the "mean free path" that an electron travels before it bumps into something and gives up its kinetic energy ought to be a sufficient counter-argument to this view. The Lynch/Cook argument is basically "I can't make it work, so it must be wrong." -- Kevin Brunt 13:54, 27 February 2006 (UTC)
replies: text: Kevin, see , and my reply in the paragraph before last.  Nigel 172.201.86.143 11:42, 1 March 2006 (UTC)

text: A more correct view is that what travels down the conductor at the velocity of propagation is not the moving electrons, but the cause of the the motion of the electrons. Since the electrons are not in mechanical contact, the mechanism that causes them to move must involve the electric and/or magnetic fields. In other words, both "Theory N" and "Theory H" apply simultaneously; the electric and magnetic fields exist because the electrons are in motion, but the electrons move because of the fields. -- Kevin Brunt 13:54, 27 February 2006 (UTC)

text: I'm not sure that there is a "standard term". I'm stressing the difference between the "charge" that flows when conventional current flows, and the underlying motion of the electrons which is what is actually creating the current flow in a metallic conductor. This is covered in a typical basic physics textbook in about two sentences, with mention of the electrons moving at a fraction of a millimetre per second, even though the effect of the current is seen (almost) instantaneously all round the circuit. The books mention the subject to disabuse students of the notion that the electrons actually move at the velocity of propagation. It is a vastly over-simplified description, but the Lynch/Catt IEE paper pretends that it is the full model that physicists use. The correct description lies not in a basic electricity textbook, but in an advanced solid-state physics textbook. However, Catt does not believe that anything outside electrical engineering is relevant, and that textbooks exist only as sources to be quoted out of context. -- Kevin Brunt 19:08, 27 February 2006 (UTC)

text: Nigel's busy over on his blog. -- Kevin Brunt 00:59, 28 February 2006 (UTC)

text: The simple answer is to just provide a reference to the Drude model. However, Nigel doesn't believe it. Whatever we do, at the end of the day we can't escape the fact that Catt's position is totally contrary to everybody else's (including Nigel, who agrees with Catt on at least some issues.) -- Kevin Brunt 00:59, 28 February 2006 (UTC)
thread_title:  Charging a TL