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In light of the lengthy discussions on this page, it now should appear obvious to everyone that the transmission line (piece of coax) acts as a capacitor of simliar physical dimensions from the points of view of
a)energy storage, (CV^2/2)
b)impedance, (Z0 of line)
c)inductance, (zero )
e)equivalent series resistance, (Z0 of line)
Wound capacitors have flat layers of conducting material either side of a dielectric. This sandwich is wound into a cylinder. THe terminations in the extended foil type are the overhanging edges of the foil. This therefore gives a transmssion line structure whose length is equal to the length of the rolled up cylinder. (a cm or two). It has been argued elsewhere on this page and not yet disproved, that a contra-fed transmission line acts in the same way as a normal transmission line as far as pulses and dc are concerned except that it can charge in half the time. Light current
Yes. I just realised when writing this piece on wound capacitors, that a steady differential voltage of 2V appears all along the line in the one way travel time of the line (ie no reflections needed to establish the steady state) (I think!)-- Light current 17:59, 15 September 2005 (UTC)
I think its obvious to us all now, but I dont think it was quite that obvious when I posed the question judging by all the posts that have been written.
Extracts from earlier posts on this subject:
No, they are not. How are they similar? — Omegatron 22:16, September 11, 2005 (UTC)
But we haven't agreed on your premise yet, LC, that the T-line is a capacitor....--Heron 12:59, 12 September 2005 (UTC)
I contend that an open-circuited (short-circuited) t-line is not equivalent to a capacitor (inductor). T.... Alfred Centauri 17:59, 13 September 2005 (UTC)
A t-line with the far end open-circuited is not equivalent to a capacitor at all.... Alfred Centauri 00:36, 13 September 2005 (UTC) NB the items in italics above are merely quotes from other posts and the other posts are still intact in their original order.-- Light current 08:57, 18 September 2005 (UTC)
Anyway, are we now all agreed that a short length of coax behaves like a small capacitor of similar length (apart from the fact that the value of the cable cap will be very small cf the manf cap)?-- Light current 22:21, 15 September 2005 (UTC)
The wound extended foil capacitor can therefore be considered as a transmission line of length equal to the length of the capacitor's cylinder and of width equal to the total length of the winding. THe signal takes 30ps with air as the dielectric to traverse the length of a 1cm long capacitor. The dielectric constant of the dielectric material used will reduce the velocity of propagation in the capcitor. A contra fed capacitor will therefore fully charge from a pulse input in the one way travel time of the signal which, with low k materials, could be around 100ps. The inductance of this capacitor with its leads removed and properly mounted in a coaxial housing will approach zero. The ESR of this capacitor will be determined by the physical dimensions of the transmission line formed by its winding.-- Light current 16:27, 15 September 2005 (UTC)
I was talking about capacitors not ideal capacitors. Case still open!-- Light current 23:58, 17 September 2005 (UTC)
My insertion is merely a quote from one of your earlier posts. Surely you do not object to that? I was quoting it only because you said that you now believed a transmission line acted as a capacitor.-- Light current 22:52, 17 September 2005 (UTC)
Yes. probaly best to use 300R twin feeder? I have to go out v. shortly, but I'll see if I can find some bits when I get home-- Light current 17:49, 15 September 2005 (UTC)
I think the setup would need to be matched to properly observe this effect, so this means a 50R to 300R balun. I have some 75R/300R baluns but im not sure of the effect of mismatch from my 50R gen to the balun i/p. Also a fiarly fast edge will be needed if a short length of cable is used. THe fastest rise I can produce/measure is about 1ns (at least thats what it looks like on my scope). I dont know the velocity factor of twin lead either but I guess were going to need quite a few feet to see much happening.-- Light current 00:09, 16 September 2005 (UTC)
You could be right- we dont know whats going to happen but I was suggesting the balun partly to convert my unbalanced gen o/p to balanced. As to the matching, maybe its not important in the transient period. I dont think we can drive this 'thing' unbalanced-- Light current 00:55, 16 September 2005 (UTC)
VF twin 300R is 0.82-- Light current 01:08, 16 September 2005 (UTC)
Im just stuck for a back to back 75R connector now!(I normally work with 50R) Ive got everything else ready , (having destroyed my FM radio aerial!) You havent got a spare you could lend me, have you?-- Light current 16:55, 17 September 2005 (UTC)
I dont know your context. So please restore them yourself but without interupting my replies. Thank you!-- Light current 22:27, 17 September 2005 (UTC)
As I said Alfred, I cant remember the order of comments that you made, except that they interrupted my replies. If would like to reorder them as you remember them, then please be my guest.-- Light current 00:06, 18 September 2005 (UTC)
I was not intending to put your comments out of context. In trying to clean up the page and move your interjections so that they did not distrurb the flow and comprehensibility of my text, I may have erroneously put your comments in the wrong place. This is quite easy to do as the mark up text doesn't look exactly the same as the page. I had no intention whatsoever of trying to twist your words and if you feel I had then you are mistaken. However, if this has upset you, I would like to apologise once more. If we could keep the integrity of each others posts, then I feel it would be beneficial. After all, Ive missed quite a few of your additions because I did not find them until I was reviewing our discussions. -- Light current 08:20, 18 September 2005 (UTC)
copied from earlier post
What about a dielectric t-line? When I say dielectric t-line, think fiber optic cable. Alfred Centauri 03:34, 14 September 2005 (UTC)
3.Is it a capacitor?
4.Is there a charge current in a dielectric t-line?
Would anyone consider that the Fabry Perot resonator is a capacitor for light energy?-- Light current 10:12, 17 September 2005 (UTC)
A Fabry-Perot resonator is a cavity formed by two mirrors on the same axis. Inside the cavity, two light waves can exist, one moving to the right, one moving to the left. The total field in the cavity is the sum of the two travelling waves. This sum is a standing wave pattern between the mirrors. For the standing waves to exist, L = m Lambda/2 where L is the length of the cavity and lambda is the wavelength in the cavity material, m is a positive integer.
If n is the refractive index of the material between the mirrors, the resonance frequencies of the resonator are given by f= mc/(2nL). THese are the longitudinal modes. The spacing between the longitudinal modes is deltaFc = c/(2Ln). This is very similar to an o/c transmssion line so I would consider in one respect at least (energy storage) that this device can act as a capacitor for light waves.-- Light current 16:09, 17 September 2005 (UTC)
For a dielectric 'transmission line' such as a FO cable, then in order to achieve the analogous situation to step waveforms entering a TEM mode conducting TL or waveguide, requires the concept of an ultra broad band source of EM radiation extending from VHF up to Xrays (say). This is because a true step requires all frequencies up to infinity to be included. Such sources do not to my knowledge exist. Also to achieve the dc energy storage phenomenon as described for the TL capacitor, would require a dielectric material of ultra wide BW. Neither do these materials exist to my knowledge. In conclusion, because a dielectric wave guide is a narrow band device it cannot support all the frequencies necessary to mimic a capacitor. It can, however, mimic a capacitor as regards energy storage over its limited BW as in the Fabry-Perot resonator.
Bearing in mind the foregoing argument, answers to ACs questions 3&4 can now be given.
Q3 It is a capacitor in the sense that it can store energy.
Q4 There is no charge current in a dielectric T line as there are no movable charges.
All in good time Alfred, all in good time!-- Light current 07:50, 18 September 2005 (UTC)
I would just like to point out the the Fabry -Perot resonator stores its energy in the oscillating EM radiation not just in the electric or magnetic fields (maybe both at once!). Im really not sure if we can call resonator an inductor as there would have to be s/c ends to reflect the radiation. I dont know what a s/c end would look like unless it was a 180 phase shifting mirror. -- Light current 18:33, 18 September 2005 (UTC)
Ideal circuit elements are used in circuit analysis. Thus, a resistor has resistance only. A capacitor has capacitance only. An inductor has inductance only. When we model non-ideal components, we combine ideal components, e.g., an inductor with a series resistance.
In circuit analysis, a capacitor is not an open circuited transmission line (TL). An inductor is not a short circuited TL, and a resistor is not a matched TL. This is because a TL is not a lumped element device. The analysis of TLs requires the full blown EM theory that circuit analysis ignores.
If full EM theory is used in the analysis of a physical circuit, we find that TLs are everywhere. The wire connecting one lead of a capacitor to a signal generator forms a TL with the other wire connected to the capacitor. A wire that is unconnected at one end is an antenna. There is radiation and there are reflections everywhere you look. This is not news to anyone (including myself) who has ever tried to get a product through EM compliance certification.
In this sense then, capacitors are TLs as are inductors, resistors, batteries, house wiring etc. etc. Everthing is a TL - Alfred is a TL - the vacuum is a TL. Heck, you don't even need conductors to have a TL. Bottom line, Maxwell's equations are valid everywhere. Thus, there is no such thing as pure capacitance, pure inductance or pure resistance. These are concepts that allow us to model physical devices so that we can actually solve and design electronic circuits and systems. When things don't quite work like we expect, it is often because we have ignored some EM effects that our model doesn't capture.
A TL is modeled with discrete ideal inductors, capacitors, and resistors. A TL is not equivalent to any one of the ideal components mentioned above. This statement is not in conflict with the statement that a physical capacitor, like any physical object, exhibits TL behaviour. Alfred Centauri 02:27, 18 September 2005 (UTC)
LC: Please, please, PLEASE try to understand that when I say something is modeled with a capacitor, inductor, and or a resistor, I am referring to the ideal components. I know I have made this point numerous times. Why don't you get it? Circuit theory is based on ideal components. Non-idealities are modeled with additional ideal components. To model a TL in circuit analysis (which does not included EM effects), we MUST use lumped ideal components as an approximation. Why do you keep coming back to this? One more time. Circuit theory does not include EM effects. TLs can only be analyzed using EM theory. To use TLs in circuit theory, we must use ideal lumped components to model them. An open-circuited TL in circuit theory is not equivalent to a (ideal) capacitor - period - case closed. If you want to model a physical capacitor in circuit theory, then by all means, add ideal components to your hearts' content until it works like you want as long as you keep in mind, there are no EM effects in circuit theory. Alfred Centauri 01:24, 20 September 2005 (UTC)
I just perused the links and what I see in these papers is that the physical capacitors referred to in the papers are modeled with cascaded lumped IDEAL elements including - you guessed it - capacitors. So, they are modeling a physical capacitor with capacitors (and other lumped elements). Doesn't that sound circular? Not to me. They are using IDEAL lumped elements to model the physical TL related effects. Alfred Centauri 02:52, 20 September 2005 (UTC)
Look at Figure 1(a) of the paper CAPpesc.pdf that you linked to. That looks a lot like our contrafeed thing doesn't it? Alfred Centauri 03:20, 20 September 2005 (UTC)
-- Light current 08:07, 18 September 2005 (UTC)
a) OK, identically constructed devices behave identically
b) OK, physical capacitors, like all physical components, exhibit TL related effects. BTW, have you considered the TL formed by the leads connecting the source to the cap?
c) I'm still working on performing this experiment on campus with some of the 'old' EM lab gear. I've also asked others to look at my 'analysis' of this thing. Alfred Centauri 01:31, 20 September 2005 (UTC)
moved to talk transmission line
Imagine an ideal current source connected across an empty (discharged) vacuum dielectric capacitor. Turn on the current source which acts as a pump for electric charge. The current source will merrily pump charge from the bottom plate to the top plate (say) and the voltage across the capacitor will ramp up. In this scenario, there are a couple of interesting questions.
1. Is any charge current actually passing between the plates.
2. Does anything pass or need to pass between the plates to allow the capacitor to charge? If so, what is it? -- Light current 15:08, 19 September 2005 (UTC)
No I meant is there anything passing directly between the plates via the dielectric? If so, what?
The information that there is charge build up on one of the plates is communicated to the other plate by the electrostatic repulsion of similar charge carriers in the other plate. So they get pushed down the wire. Yes?? So what passes between the plates is information in the electric field?-- Light current 03:17, 20 September 2005 (UTC)
Exactly, O, but what AC and I are trying to establish here is the necessity (or not) of displacement current in capacitors. He say YO! (probably), I say -- dont know!. So we're just working thro the argument step by step. Any insights you have along the way would be interesting.-- Light current 12:25, 20 September 2005 (UTC)
Are you trying to say that the magnetic field, if it existed in the (open circuit from a low freq POV) system would then collapse?
Im going to think about this very carefully before I answer.-- Light current 15:03, 20 September 2005 (UTC)
Let me get you straight. Are you saying that as each new 'electron' or packet of charge reaches the top plate, then the electric field between the plates jumps up a bit? Is so I would agree. Is this your sudden change in electric field?-- Light current 15:21, 20 September 2005 (UTC)
I think I see what you may be getting at. As the charge difference builds up on the plates, an increasing electric field is produced between them. According to old J.C. Maxwell, a changing electric field here produces a magnetic field that is propagated into space at the speed of light outward from the capacitor plates and with the changing electric field you get some EM radiation.(traveling magnetic waves cannot exist alone - can they?) Now I think E x H gives the direction of the radiation and this would appear to be radial from an axis perpendicularly joining the centres of the capacitor plates, Yes? So nothing is actually passing between the plates yet then?
But heres an interesting thought: Assume that this radiation is indeed radial and assume we have a circular parallel plate capacitor. Also assume that this radiation starts from the centre of the capacitor (where else could it start?) When the travelling EM wave reaches the periphery of the capacitor discs it sees an *open circuit* so what happens to it? ;-)-- Light current 15:46, 21 September 2005 (UTC)
Let me try to offer some suggestions here. It seems you are having trouble because your second differetial of E is zero. Right? However, the charge flow cannot start infinitely slowly. Neither can it end infinitely slowly. So there will be a non zero 2nd diffl at the the start and end of the charging period, does that help at all?-- Light current 22:43, 26 September 2005 (UTC)
Yes, I understand what you are trying to do now. THe radiation maybe constant but IMHO it cant escape the interior of the capacitor because it sees an o/c at the ends. Do you agree with me on that one?-- Light current 23:21, 26 September 2005 (UTC)
Just a simple question here. Are you both sure that charges in the wire or on the plates come to rest very quickly? Or do they slow down gradually as they meet more of thier friends? (electr static repulsion). I suggest that the only thing going fast here is the EM energy (parallel to the plates of the capacitor). It travels at the speed of light in the medium. There is minimal effect due to charges decelerating because they're not travelling very fast in the first instance!-- Light current 00:46, 5 October 2005 (UTC)
No. The whole point of this discussion is to show (hopefully) that no charge needs to move to get EM radiation. That this is so only requires consideration of EM propagation in vacuo.-- Light current 01:24, 5 October 2005 (UTC)
Also, I can't see how you can get very high time rates of change of charge density if you dont have the actual charges moving at the same high rates (even at the (sub)atomic scale). I also notice that you have sneaked the concept of displacement current back into the argument. This has not been proven to exist. In short, I think there is no cat up your tree!(Woof! Woof!) [3]-- Light current 01:36, 5 October 2005 (UTC)
If charge cannot move at 'c', what is your mechanism for the actual charge density wave to propagate at 'c'. You are trying to find a mechanism for how ordinary current (the slow movement of charge carriers) converts into EM radiation. It cannot directly be due to the acceleration of the charge carriers as has been calculated by Pfalsted. Therefore there must be another process. (Unless of course the EM energy is already there in another guise, like dc? Refer to my original question about diff between EM and dc)-- Light current 15:07, 5 October 2005 (UTC)
You definitely need movement of charge to get radiation. Pfalstad
Where does this moving 'charge' come from in a vacuum borne EM wave? Are you just talking about the initial generation of that wave in a conductor system? Propagation of Electromagnetic waves doesnt involve charges moving does it?. If you are talking about the generation of EM waves in an aerial system, this seems to be what AC is talking about (as far as I can tell) and this seems to be what AC is trying to work out. i, on the other hand, do not offer any explanation of How charge current is converted to EM radiation. My suggestion is that the EM radiatiopn and actual charge current are (almost totally) independent of each other. Take a battery, and a parallel pair of wires connecting the terminals to a load resistor via a switch. We know that the energy travels at'c' but the charges travel much more slowly. You will probably say: Ah yes-- but the charge density wave travels at 'c'.In that case, I must repeat my earlier question which was: what is your mechanism for describing light speed travel of charge density? Or to put it another way, what is it actually that travels at light speed to cause these fluctuations in the charge density on the wire. The answer of course can be only one thing: EM radiation flowing between the wires (not in them) -- Light current 21:25, 5 October 2005 (UTC)
Ah.my dear Pfalstad. Yes. I agree with the above post of yours. What Ive been trying to explian to Alfred (not very sucessfully) is that it is the EM wave that is fundamental and the current, mag field etc are all a result of that. I suppose you could say that the EM wave drags along the charges as fast as they will go. When a capacitor is charging slowly is when I have a slight problem because I cant see the mechanism by which 1 electron per half hour say arriving at the top plate can give rise to all the effects that Alfred seeks especially when you have both almost agreed that the electron deceleration can give only a tiny amount of radiated power. The only possible solution I can see is that each electron, as it arrives, is accompanied by a tiny amount of EM radiation (which has actually dragged it along). This radiation flows into the top plate and sets up a standing wave of very small amplitude travelling from one end of the plates to the other end and back again.. As more and more electrons arrive,(againg accompnied by their associated EM energy) the standing wave amplitude in the capacitor slowly builds (in a linear manner if current fed). Of course, if the EM adds non coherently (out of phase) in the transmission line between the capacitor plates, the voltage produced across the plates will show some noise (if you had anything sensistive enough to see it).I'm not sure whether it does or not. I would be interested to know what you think of this suggestion.-- Light current 23:57, 5 October 2005 (UTC)
Please dont call my ideas ludicrous. If you think they are wrong, disprove them. My previous statement about charges being dragged along was very sloppy (made without due thought)and I retract it. The charges in the conductors are induced in the surface of the conductors and therefore dont need to move along the wire in the direction of the energy vector. So do charges play any part in energy transfer at all? If you are preparerd to listen to my arguments without trying to score points or deride my attemts at explanation, imply I'm a crank etc, I will be happy to try to explain my viewpoint. Whether you or others agree is up to you/them. But if not, it will be incumbent upon those persons to demolish my arguments one by one not just try to dismiss them as cranky thoughts-- Light current 19:26, 8 October 2005 (UTC)
moved to talk:transmission line
Im not going to go as far as saying an electron is ONLY an EM wave. As we have established earlier, it seems no one knows exactly of what an electron consists. However, certain of its attributes may be explainable in terms of EM waves.-- Light current 16:53, 13 October 2005 (UTC)
We still have something of a paradox here. We know for instance in a real TL travelling waves produce losses due to skin effect, but in a situation we have just described, we find zero or very low losses. Can you say why?.
Well I say my model is correct. The reason there are no losses is that there is no net current. This therefore lines up with the actual situation of a charged TL.-- Light current 03:15, 13 October 2005 (UTC)
However, the importance of this apparent duality of EM waves and steady dc, in my mind, cannot be underestimated. It should have impressed you also, although you seem remarkably blase about it!. If the duality is accepted, it has far reaching consequences on the nature of those things we call voltage and current. I will leave the idea with you a little longer before suggesting applications and ramifications of this duality idea.-- Light current 17:47, 12 October 2005 (UTC)
BTW, if you had been taught this idea at university, college, would you have believed it?-- Light current 18:11, 12 October 2005 (UTC)
Sorry, I thought I had described what the point was. Obviously you do not wish to accept the implications.-- Light current 01:57, 13 October 2005 (UTC)
OK heres one. Is a simple battery a source of dc only, or is it also a source of EM radiation. Please think crefully before answering! ;-)-- Light current 17:10, 13 October 2005 (UTC)
Heres some more thoughts. What function do the charges on the transmission line conductors have in the transmission of the EM energy back and forth in the line. Do they need to be mobile carriers? Do they need to move?. Do they need to be there at all.? I think I can answer these questions, but I leave it to you or AC to comment first -- Light current 17:37, 13 October 2005 (UTC)
Of course, one would normally say that a battery is not a source of EM radiation at all. However if steady dc can be represented as counter propagating waves then one must ask the question. THe reasons you give for the necessity of mobile charge carriers in the TL are not logical. For instance, its possible to have charge separation in a dilectric is it not? Im not saying electrons dont exist! Your last sentence, maybe, highlights the difficulty with the idea: ie if these waves cannot be distinguished from steady dc, what does that mean?
There are a few conclusions one could draw.
a) a transverse electrostatic field in a TL CAN be generated by an initial one way flow of energy as when charging, and then maintained by the counter propagating EM waves. (showing some equivalence between EM and dc.)
OR b)travelling EM waves do not exist in the TL at any time. So how does the energy get there?
OR c) travelling waves are initially used to charge the capacitor but when charged, the waves stop moving suddenly. But how do they do that? ie what is the exact mechanism by which they are stopped- and stopped instantaneously at that?
AS I said before, things that cannot be distinguished as different my any method whatsoever might as well be considered the same. Whether they are truly the same or not is a philosophical question, not one of physics.-- Light current 17:17, 16 October 2005 (UTC)
Could you say what you mean by that in plain English please?-- Light current 01:53, 13 October 2005 (UTC)
The fields we are considering are not in free space, the electric field exists between the two conductors. I didnt say anything about the charge densities on the conductors. AC I dont think your above statement says a great deal. We have a steady (dc) electric field. But we also have two counter propagting ac waves that have been show to add up to the dc version. Does this worry you at all?-- Light current 16:17, 13 October 2005 (UTC)
You haven't shown anything as far as I am concerned. You have made some hand-waving arguments that aren't very good and you believe that you to have shown something? Do you consider this rigorous? Please show mathematically what you claim to be shown. Do you agree that the electric field between the conductors of the charged TL is due to the net electric charge on the conductors? The conservative part of the electric field is, by Gauss's law, due to electric charge. The non-conservative part of the field is due to changing magnetic flux. Potential difference (voltage) has meaning only for a conservative field. The voltage across the conductors of the charged TL must be due to a conservative field. This field can only be created by electric charge. Alfred Centauri 17:44, 13 October 2005 (UTC)
I am trying to find a way of explianing this waveform thing mathematically using Heaviside functions. But I need to do some research first.-- Light current 21:43, 15 October 2005 (UTC)
Since this aspect seems to be causing a lot of controversy with regard to the validity of my arguments on the transmission line circuit, I am going to try to answer all the points opn this aspect that have been made. To do this I must go back and review all the posts (mainly from AC) so I know exaactly what the objections and comments are. I therefore hope that AC and other interseted perties will bear with me whilst I do this revision and compose a reply. Thank you for your patience.-- Light current 01:30, 14 October 2005 (UTC)
By studying some of your earlier posts on the generator problem AC, Maybe I can cut short the discourse by saying the following:
Let the generator remain connected for all time after the initial connection. At the time of arrival of the reflected wave front, there is 2V from the gen, and 2V on the line. Now what is the current thro Rs (the generator source resistance)? Zero!. So from the point of view of the wave, what impedance does it see? Infinity. So what does that mean? Is it a short, open or matched?
The resistance of a resistor is still the same if its in the drawer, but that doesnt mean it has any effect. Think of bootstrapping. Actually, come to think of it, it doesnt really matter what the impedance is after the lines charged as long as the gens still connected. It could be zero, 50ohms of infinity as far as the signal is concerned. Thats because no current can flow thro this resitor. So it can be defined as anything you like. But its not connected to ground - its connected to 2V. The wave incident at this resistor cant push any current thro it. (cos theres 2V on the other side. The wave couldnt push any current thro an o/c if that was there instead could it?. So as far as the wave's concerned, it might as well be an o/c. Also, this must be true, otherwise the wave would pass current thro the resistor and the reflection would be less than it actually is. THat would mean there would not be 2V on the line after 2T. Can you see it now? I dont think there are many other ways to explain it. T
The standard way of testing the impedance is to look at the reflected signal. rho = (Zl-Zo)/(Zo+Zl) where rho is the reflection coefficient.(reflected ampl /incident ampl), Zl is the load resistor. In our case, rho=+1 (all refelected with no inversion), yes?- so you can work out Zl for yourself.-- Light current 06:36, 16 October 2005 (UTC)
No. The applet is completely correct. Thats what I ve been saying all this time. THe applet shows the total voltage on the line which is made up up of the sum of each traveling wave. (V+V=2V). I shows the two travleing waves add to give dc! BTW a TL can have a waves travelling in both diections simultaneously but Im sure you knew that.-- Light current 19:07, 16 October 2005 (UTC)
I know thats the way you prefer, but its not correct because energy is still flowing behind the wave front. That this is so can be seen because until the reflected wave reaches the near end again, energy is still being pumped in to the line from the generator and all waves are travelling!-- Light current 21:09, 16 October 2005 (UTC)
If you were taught that the 'Changing part' or any other part of the wave is absorbed by the teremination, I think that is definitely wrong or you may have misunderstood it. How can the termination absorb energy? (I^2*R*t) - there's no current in it (as I have said before!) Once the line's charged, yes the energy input into the line stops, but the waves inside the line carry on traveling. If they dont, can you describe how they are stopped?-- Light current 21:50, 16 October 2005 (UTC)
If you dont know how the waves are stopped, why not just say so. I dont know how they can be stopped either. But its just possible that they are in fact stopped and we have discovered something new! -- Light current 22:00, 16 October 2005 (UTC)
But a resistor would only absorb some energy, not stop the waves. Then we would be short of energy on the line. This does not happen in the real case. EM waves can be generated and absorbed. THey cannot be stopped! What does a stopped EM wave imply? It cannot be sustained. It must travel to live!-- Light current 22:24, 16 October 2005 (UTC)
If the length of the resistor is troublesome, imagine instead a current source with a parallel matching disc resistor of infinitesimal thickness connected actually in the coax line from inner to outer. In this case of course, the current source would need to keep pumping to provide the essential mismatch at the near end. I repeat that the resistor cannot absorb the wave. If it did, it would absorb all the energy that we had just put into the line, and the line would never charge up. Just have a think about it a while. Also, if the edge reaching the near end after reflection is not perfectly square, the generator merely turns off a bit more slowly to correct the situation. Its a bit like unity feedback in a way.
If you dont accept the basic argument, I dont see what difference a load of math (necessarily based on the same argument) will make. Nevertheless, if I do come up with an alternative explanation you will see it here.-- Light current 03:07, 17 October 2005 (UTC)
OK just one last try on the qualitative argument. THe voltage source with internal resistance Zo is left connected to the line for all time.
Lets assume you are correct in that the source resistance does indeed absorb the refelected wave. But if you allow that, you must accept that it absorbs all of the reflected travelling wave from the line, not just some of it. OK? Right, now in this way of looking at it, the generator continues to send energy down the line for ever and a day, but absorbs this energy after its round trip when it gets back. The line is fully charged and cant accept any more energy. In this way of looking at it, the line is still fully charged, waves are counter propagting up and down the line, and the line is terminated in its characteristic impedance. Happy?-- Light current 03:30, 17 October 2005 (UTC)
If I have missed an important part of your argument, please let me know and I'll go back and look again at your earlier posts on this aspect.-- Light current 02:14, 14 October 2005 (UTC)
Thank you for your courtesy in replying swiftly to my last post. It will save me a great deal of work in preparing answers. I have enjoyed this discussion, and I'm sorry I couldn't convince you of my ideas. We will therfore have to agree to disagree! If I can think of a mathematical proof I will surely publish it here-- but dont hold your breath!-- Light current 04:40, 14 October 2005 (UTC)
If you consider pulse charging of this capacitor, you will see that the traveling waves do indeed add up to dc. Get a battery and a capacitor. Connect them, then measure the capacitor voltage. Its dc! But EM waves have been used to put the energy there.-- Light current 18:01, 8 October 2005 (UTC)
How do the EM fields become established then if not by EM waves?-- Light current 20:49, 8 October 2005 (UTC)
Just another thought. A battery charging a capacitor transfers energy to the capacitor. Right? How does the energy travel from the battery to the capacitor? (Not thro the wires)-- Light current 19:12, 8 October 2005 (UTC)
Im not sure to which idea of mine you (AC) are specifically referring. Is it the one about energy flowing in the space between the wires or the fact that EM radiation is more fundamental than current?. Any way I thought you were having a Wikibreak! -- Light current 01:36, 6 October 2005 (UTC)
I keep telling you - I'm not a physicist!-- Light current 00:36, 6 October 2005 (UTC)
I'm not trying to tell you anything. I am putting forward some ideas which I believe have some merit for discussion. (BTW I was trying to move the argument forwards with Pfalsted in the understanding that you had temporaily retired from the ring). Yes I admit that communication has been difficult between us. Thats probably because your EM theory etc is far in advance of mine. I have to rely on my meagre (and outdated) knowledge and some common sense. The standard argumnets relating to capcitors charging and the details of EM radiation, how charge is carried by an electron etc do not satisfy me. I'm sure they dont satisfy you either. I am not trying to yank your chain as you put it but to try to develop my (albeit far less than perfect) thoughts on these matters with the help of yourself and others of superior intellect to mine. You mustn't expect everyone to be as smart as you are! THats it Im clean now!-- Light current 01:58, 6 October 2005 (UTC)
OK, AC. I understand that you are not considering displacement current at the moment, but EM radiation due to accelerated charges (which is virtually nil- we think). So that leaves the tricky question of what actually passes between the plates of the capcitor if its not radiation.
BTW If you do decide to consider 'displacement current' in the future, could you please say whether its the sort that Maxwell defined, or the sort that is supposed to accompany propagating EM waves. I think this will save much confusion. THank you!-- Light current 22:07, 5 October 2005 (UTC)
Moved discussion to Wikipedia Talk:WikiProject Electronics
It says the main reason for using oil in old large capacitors and transformers is because of the heat generated. Funny, I thought it was used mainly as an insulating medium and dielectric.-- Light current 02:38, 20 September 2005 (UTC)
OK, its for cooling as well!-- Light current 03:23, 20 September 2005 (UTC)
But not mainly for cooling in capacitors as they shouldnt get very hot (unless thers a lot of ripple current and a high ESR). So I intend to correct this statement.-- Light current 14:33, 20 September 2005 (UTC)
Ive posted a dispute tag in this area, because I dont believe in general that oil is used for capacitor cooling. Quote from manufacturer literature:
'# Why are GAEP high voltage capacitors oil-filled?
Highly insulating oil is used to suppress partial discharges (corona), increase the dielectric strength, and increase the effective permittivity (dielectric constant) of the capacitor dielectric. Oil-filled film capacitors have high energy density in comparison with other types of capacitors used at high voltage, such as ceramic capacitors. Different types of oils are used with different types of capacitor dielectric and electrode designs. '
-- Light current 00:37, 26 September 2005 (UTC)
Remember the oil filled transformers that contain the special transformer oil and the large theory associated with it. -- Davy Jones 01:19, 11 October 2005 (UTC)
Pardon?-- Light current 15:48, 11 October 2005 (UTC)
Why? This page is about capacitors.-- Light current 01:53, 12 October 2005 (UTC)
This is another new one on me. I didnt know that low ESR was essential for integrator capacitors. Did the author really mean leakage current? I think he did, but Im willing to be persuaded otherwise.-- Light current 22:05, 3 October 2005 (UTC)
I would suggest that the effect of capacitor ESR in integrators is minimal. THe leads you use to connect the capacitor have probably got more resistance than a half decent caps ESR (0.0001 ohm say)-- Light current 23:27, 3 October 2005 (UTC)
Just looking at manufacturers websites. Low ESR caps are about 0.01 ohm (10milliohm). So I was only 2 orders of magnitude out.!! ESR seems to go down with increasing frequency. Not sure why.-- Light current 22:20, 8 October 2005 (UTC)
Whats the resistance of 1" of 1oz copper PCB track say 10 thou wide? (in milliohms).-- Light current 23:39, 13 October 2005 (UTC)
I think this page is getting near to being good enough to be considered as a featured article. But is it too long for that. Any comments?-- Light current 14:40, 5 October 2005 (UTC)
Well Davy Jones, (un?)fortunately, this sort of stuff is not accepted by the community at large and is considerd new research!. As such it cant really be incorporated into WP articles. My purpose here on Talk is to try to get editors thinking critically in order to sharpen up their skills for the purpose of creating great, accurate and easy to understand articles.-- Light current 18:17, 12 October 2005 (UTC)
Since I have now started the long awaited (by some) page on Ivor Catt, I wonder if we should move all the discussions about Catt related subjects on this page to Talk:Ivor Catt. Could we have some comments please ASAP-- Light current 14:05, 15 October 2005 (UTC)
OK I'll just wait for one or two agreements from our project team before proceeding!-- Light current 21:31, 15 October 2005 (UTC)
Do we need these pictures her or would they be better on the practical capacitors page? -- Light current 01:25, 22 November 2005 (UTC)
In capacitors when newly electrons (of charge -Q) approaches one plate it will experience of force of repullsion from the negatively charged plate, and this increases their potential energy and the potential across the capacitor will increase But as -Q approaches, -Q from the opp plate will get repelled (inducing a +Q on the plate),
The question now if this is happened shouldnt the potential of the capacitor becomes constant because as ΔPE comes from -Q on one plate shouldnt ΔPE is lost (or transferred) from the opp plate
-- Ducky12345 ( talk) 16:19, 2 March 2008 (UTC)
The information isn't trivia, rather, it shows how the layperson may conceptualize the use of the word. Zaphraud ( talk) 20:03, 21 October 2008 (UTC)
Ccrrccrr ( talk) 12:08, 24 October 2008 (UTC)
When I'm logged in the images show up in the right place, but when logged out the images appear ontop of the text like in this screen shot of Capacitor. There are blank spots in the text where the images are supposed to appear further down the page. This is with Firefox 2.0 on osx. Autopilot ( talk) 01:39, 24 November 2008 (UTC)
This article is the WP:WikiProject Electronics collaboration for December 2008 to January 2009. Please suggest and claim responsibility for improvements here. Please don't use this section to discuss improvements, so new editors can easily participate. Potatoswatter ( talk) 23:57, 14 December 2008 (UTC)
Rename "filtering" section to reflect exclusion of signal filtering. - [anon]
I'll take on the unideal bahaviour section if that's ok with everyone. SpinningSpark 00:30, 15 December 2008 (UTC)
<- As I said, I'm quite neutral about this. The consensus in textbooks and in this discussion lies with the charge integral, so let's stick with that. I only intended this to be a brief talking point and it's probably time to move on to something else! Papa November ( talk) 14:20, 20 December 2008 (UTC)
This article starts with "a capacitor... is a passive electrical component". That's much too narrow a definition for an article that is simply called "capacitor": it is simply any pair of conductors separated by a dielectric. The article then focuses entirely upon man-made capacitors, and their applications in Electronics. We could expand and rewrite the article to include natural capacitors, and avoiding putting undue weight on man-made devices.
Alternatively, we could do the following:
Opinions? Papa November ( talk) 15:29, 20 December 2008 (UTC)
Sections for topics that are tangential here and already covered in other articles, like displacement current, we should possibly move to capacitor/deprecated sections. Potatoswatter ( talk) 04:35, 22 December 2008 (UTC)
I mostly recall seeing in textbooks but permittivity and this article use . Which do we prefer? I vote for the one which isn't a "variable" but I'm not really informed in these matters. Potatoswatter ( talk) 02:21, 21 December 2008 (UTC)
The main article for microphony as an undesirable effect is microphonics (although it is not a very substantial article). Condenser microphone is certainly the same physical effect but is not really in the context of non-ideal. Do you want that changed? SpinningSpark 12:20, 21 December 2008 (UTC)
There's a whole mess of other articles about capacitors. (Guess they're pretty sexy.) I think it would be a good idea to keep our eyes open and make sure they're all in the category. A number of them should be merged into electrolytic capacitor. Potatoswatter ( talk) 04:08, 22 December 2008 (UTC)
Uh, "The common parallel plate model reduces such a capacitor to a one-dimensional cross section." I know nothing about capacitors, but wouldn't two broad plates separated by a small distance be commonly modeled in two dimensions? (heck, the picture uses three). If the sentence is truly about a one-dimensional mathematical model, wouldn't it be better placed well before the intro of the concept of parallel plates? — Joel D. Reid ( talk) 04:23, 27 December 2008 (UTC)
Would the other editors taking part in this collaboration be agreeable to putting this article up for GA review. I don't have a great deal of experience of this, but when I have been through it before the main things are that [1] you keep monitoring the review as it progresses so that problems are dealt with in a timely manner (otherwise the reviewer loses interest and goes away) and [2] absolutely everything has to be referenced, ie every para. If you are all prepared to work on the article at this level I propose putting it up.
Also, I think the ESR section needs some work, the maths looks gastly. A diagram would help to simplify it. I will work on that bit if there are no objections. SpinningSpark 20:51, 5 January 2009 (UTC)
"Capacitors were discovered in glass jars in 1745 . . ."? How about "The first form of capacitor was the Leyden jar, invented in 1745 . . ." -- Chetvorno TALK 15:55, 29 January 2009 (UTC)
Friends, i am a HT consumer in india. in our montly billing our power factor is only 0.89. it has been advised by the electricity board people to add capacitors in our circuit. i wish to kno how the rating of the capacitor is arrived at and also how this has to be connected in the circuit.i heard that extra precautions need to be taken while switching on the Generator. i heard while switching on the circuit the capacitor needs to be disconnected.please throw some light on this. —Preceding unsigned comment added by 59.90.213.170 ( talk) 13:16, 11 March 2009 (UTC)
In looking through electronic catalogs, I see that certain electrolytic capacitors are referred to as “Snap-In” capacitors, but I do not know what that means. Does it refer to a socket type - or what? An explanation would be appropriate for this article. I am sure that some thought could be give to expand this article to include definitions for many of the jargon words pertaining to capacitors. Stan ( talk) 18:00, 13 April 2009 (UTC)
In the last section:
Capacitors used in RF or sustained high-current applications can overheat,
What does RF stand for? A quick google search didn't turn up something useful. Perhaps someone can add it to the article. Thanks Panoramix303 ( talk) 22:24, 22 May 2009 (UTC)
Radio frequency. SpinningSpark 23:12, 22 May 2009 (UTC)
wat's difference between polarised and non-polarised capacitors and their functions? —Preceding unsigned comment added by 115.99.0.27 ( talk) 08:48, 29 June 2009 (UTC)
I made a photo of a variable capacitor made of 2 wires near each other in a frame:
At least that's what I think this is supposed to be. Not sure, if another picture of a cap improves these articles, but this one clearly shows the "inside" of a cap. You may add it to the articles Capacitor, Types_of_capacitor and/or Variable_capacitor.
Should I trim the irrelevant stuff from this image?
I am an educated person, though not in physics. (I took undergrad courses in physics & calculus ~15 years ago, but my PhD is in nutrition.)
I am now training as a volunteer at a large science museum where I live. I will be conducting demonstrations for tour and family groups (mostly kids), including a demonstration on static electricity. Part of the demonstration uses Leyden jars. In my search for more information about how Leyden jars work, I have been frustrated by technical articles describing ratios of charge to potential differences and such when what I really wanted to know was where the electrons went and how the charge was changed on the outer plate in response to the inner plate. Does the outer plate have to be grounded to allow the opposite charge to accumulate? Or is it a partial charge resulting from electron movement within the plate itself? What determines the voltage of an arc caused by touching the pole? Is it a simple matter of how many electrons are stored in one plate or the other? (I'm not looking for these answers on this talk page, just listing the kinds of questions I wanted to learn about in the article but had difficulty with. No need to respond directly to these questions here on the talk page.)
I just want you knowledgeable and talented physics and math people to know that this one guy (me) had a really difficult time learning what I wanted to know from this page, and I want to ask you all to consider presenting information here in a manner that might be more understandable to people like me who aren't that strong on our physics or calculus. I think a kid working on a transistor radio in shop class should be able to take away at least basic knowledge of how capacitors function. I appreciate the fact that all of this technical information is here for anyone who wants to learn the details, but please consider writing a basic description of the principles with us laypeople in mind -- maybe in its own section.
But please don't think of this as a harsh criticism. I truly do appreciate the work you've all done to bring an enormous amount of information to the Wikipedia knowledge base! Someday I might want to brush up on my physics & learn this stuff properly. Dcs002 ( talk) 01:01, 10 October 2009 (UTC)
![]() | 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. |
Archive 1 | Archive 2 | Archive 3 | Archive 4 |
In light of the lengthy discussions on this page, it now should appear obvious to everyone that the transmission line (piece of coax) acts as a capacitor of simliar physical dimensions from the points of view of
a)energy storage, (CV^2/2)
b)impedance, (Z0 of line)
c)inductance, (zero )
e)equivalent series resistance, (Z0 of line)
Wound capacitors have flat layers of conducting material either side of a dielectric. This sandwich is wound into a cylinder. THe terminations in the extended foil type are the overhanging edges of the foil. This therefore gives a transmssion line structure whose length is equal to the length of the rolled up cylinder. (a cm or two). It has been argued elsewhere on this page and not yet disproved, that a contra-fed transmission line acts in the same way as a normal transmission line as far as pulses and dc are concerned except that it can charge in half the time. Light current
Yes. I just realised when writing this piece on wound capacitors, that a steady differential voltage of 2V appears all along the line in the one way travel time of the line (ie no reflections needed to establish the steady state) (I think!)-- Light current 17:59, 15 September 2005 (UTC)
I think its obvious to us all now, but I dont think it was quite that obvious when I posed the question judging by all the posts that have been written.
Extracts from earlier posts on this subject:
No, they are not. How are they similar? — Omegatron 22:16, September 11, 2005 (UTC)
But we haven't agreed on your premise yet, LC, that the T-line is a capacitor....--Heron 12:59, 12 September 2005 (UTC)
I contend that an open-circuited (short-circuited) t-line is not equivalent to a capacitor (inductor). T.... Alfred Centauri 17:59, 13 September 2005 (UTC)
A t-line with the far end open-circuited is not equivalent to a capacitor at all.... Alfred Centauri 00:36, 13 September 2005 (UTC) NB the items in italics above are merely quotes from other posts and the other posts are still intact in their original order.-- Light current 08:57, 18 September 2005 (UTC)
Anyway, are we now all agreed that a short length of coax behaves like a small capacitor of similar length (apart from the fact that the value of the cable cap will be very small cf the manf cap)?-- Light current 22:21, 15 September 2005 (UTC)
The wound extended foil capacitor can therefore be considered as a transmission line of length equal to the length of the capacitor's cylinder and of width equal to the total length of the winding. THe signal takes 30ps with air as the dielectric to traverse the length of a 1cm long capacitor. The dielectric constant of the dielectric material used will reduce the velocity of propagation in the capcitor. A contra fed capacitor will therefore fully charge from a pulse input in the one way travel time of the signal which, with low k materials, could be around 100ps. The inductance of this capacitor with its leads removed and properly mounted in a coaxial housing will approach zero. The ESR of this capacitor will be determined by the physical dimensions of the transmission line formed by its winding.-- Light current 16:27, 15 September 2005 (UTC)
I was talking about capacitors not ideal capacitors. Case still open!-- Light current 23:58, 17 September 2005 (UTC)
My insertion is merely a quote from one of your earlier posts. Surely you do not object to that? I was quoting it only because you said that you now believed a transmission line acted as a capacitor.-- Light current 22:52, 17 September 2005 (UTC)
Yes. probaly best to use 300R twin feeder? I have to go out v. shortly, but I'll see if I can find some bits when I get home-- Light current 17:49, 15 September 2005 (UTC)
I think the setup would need to be matched to properly observe this effect, so this means a 50R to 300R balun. I have some 75R/300R baluns but im not sure of the effect of mismatch from my 50R gen to the balun i/p. Also a fiarly fast edge will be needed if a short length of cable is used. THe fastest rise I can produce/measure is about 1ns (at least thats what it looks like on my scope). I dont know the velocity factor of twin lead either but I guess were going to need quite a few feet to see much happening.-- Light current 00:09, 16 September 2005 (UTC)
You could be right- we dont know whats going to happen but I was suggesting the balun partly to convert my unbalanced gen o/p to balanced. As to the matching, maybe its not important in the transient period. I dont think we can drive this 'thing' unbalanced-- Light current 00:55, 16 September 2005 (UTC)
VF twin 300R is 0.82-- Light current 01:08, 16 September 2005 (UTC)
Im just stuck for a back to back 75R connector now!(I normally work with 50R) Ive got everything else ready , (having destroyed my FM radio aerial!) You havent got a spare you could lend me, have you?-- Light current 16:55, 17 September 2005 (UTC)
I dont know your context. So please restore them yourself but without interupting my replies. Thank you!-- Light current 22:27, 17 September 2005 (UTC)
As I said Alfred, I cant remember the order of comments that you made, except that they interrupted my replies. If would like to reorder them as you remember them, then please be my guest.-- Light current 00:06, 18 September 2005 (UTC)
I was not intending to put your comments out of context. In trying to clean up the page and move your interjections so that they did not distrurb the flow and comprehensibility of my text, I may have erroneously put your comments in the wrong place. This is quite easy to do as the mark up text doesn't look exactly the same as the page. I had no intention whatsoever of trying to twist your words and if you feel I had then you are mistaken. However, if this has upset you, I would like to apologise once more. If we could keep the integrity of each others posts, then I feel it would be beneficial. After all, Ive missed quite a few of your additions because I did not find them until I was reviewing our discussions. -- Light current 08:20, 18 September 2005 (UTC)
copied from earlier post
What about a dielectric t-line? When I say dielectric t-line, think fiber optic cable. Alfred Centauri 03:34, 14 September 2005 (UTC)
3.Is it a capacitor?
4.Is there a charge current in a dielectric t-line?
Would anyone consider that the Fabry Perot resonator is a capacitor for light energy?-- Light current 10:12, 17 September 2005 (UTC)
A Fabry-Perot resonator is a cavity formed by two mirrors on the same axis. Inside the cavity, two light waves can exist, one moving to the right, one moving to the left. The total field in the cavity is the sum of the two travelling waves. This sum is a standing wave pattern between the mirrors. For the standing waves to exist, L = m Lambda/2 where L is the length of the cavity and lambda is the wavelength in the cavity material, m is a positive integer.
If n is the refractive index of the material between the mirrors, the resonance frequencies of the resonator are given by f= mc/(2nL). THese are the longitudinal modes. The spacing between the longitudinal modes is deltaFc = c/(2Ln). This is very similar to an o/c transmssion line so I would consider in one respect at least (energy storage) that this device can act as a capacitor for light waves.-- Light current 16:09, 17 September 2005 (UTC)
For a dielectric 'transmission line' such as a FO cable, then in order to achieve the analogous situation to step waveforms entering a TEM mode conducting TL or waveguide, requires the concept of an ultra broad band source of EM radiation extending from VHF up to Xrays (say). This is because a true step requires all frequencies up to infinity to be included. Such sources do not to my knowledge exist. Also to achieve the dc energy storage phenomenon as described for the TL capacitor, would require a dielectric material of ultra wide BW. Neither do these materials exist to my knowledge. In conclusion, because a dielectric wave guide is a narrow band device it cannot support all the frequencies necessary to mimic a capacitor. It can, however, mimic a capacitor as regards energy storage over its limited BW as in the Fabry-Perot resonator.
Bearing in mind the foregoing argument, answers to ACs questions 3&4 can now be given.
Q3 It is a capacitor in the sense that it can store energy.
Q4 There is no charge current in a dielectric T line as there are no movable charges.
All in good time Alfred, all in good time!-- Light current 07:50, 18 September 2005 (UTC)
I would just like to point out the the Fabry -Perot resonator stores its energy in the oscillating EM radiation not just in the electric or magnetic fields (maybe both at once!). Im really not sure if we can call resonator an inductor as there would have to be s/c ends to reflect the radiation. I dont know what a s/c end would look like unless it was a 180 phase shifting mirror. -- Light current 18:33, 18 September 2005 (UTC)
Ideal circuit elements are used in circuit analysis. Thus, a resistor has resistance only. A capacitor has capacitance only. An inductor has inductance only. When we model non-ideal components, we combine ideal components, e.g., an inductor with a series resistance.
In circuit analysis, a capacitor is not an open circuited transmission line (TL). An inductor is not a short circuited TL, and a resistor is not a matched TL. This is because a TL is not a lumped element device. The analysis of TLs requires the full blown EM theory that circuit analysis ignores.
If full EM theory is used in the analysis of a physical circuit, we find that TLs are everywhere. The wire connecting one lead of a capacitor to a signal generator forms a TL with the other wire connected to the capacitor. A wire that is unconnected at one end is an antenna. There is radiation and there are reflections everywhere you look. This is not news to anyone (including myself) who has ever tried to get a product through EM compliance certification.
In this sense then, capacitors are TLs as are inductors, resistors, batteries, house wiring etc. etc. Everthing is a TL - Alfred is a TL - the vacuum is a TL. Heck, you don't even need conductors to have a TL. Bottom line, Maxwell's equations are valid everywhere. Thus, there is no such thing as pure capacitance, pure inductance or pure resistance. These are concepts that allow us to model physical devices so that we can actually solve and design electronic circuits and systems. When things don't quite work like we expect, it is often because we have ignored some EM effects that our model doesn't capture.
A TL is modeled with discrete ideal inductors, capacitors, and resistors. A TL is not equivalent to any one of the ideal components mentioned above. This statement is not in conflict with the statement that a physical capacitor, like any physical object, exhibits TL behaviour. Alfred Centauri 02:27, 18 September 2005 (UTC)
LC: Please, please, PLEASE try to understand that when I say something is modeled with a capacitor, inductor, and or a resistor, I am referring to the ideal components. I know I have made this point numerous times. Why don't you get it? Circuit theory is based on ideal components. Non-idealities are modeled with additional ideal components. To model a TL in circuit analysis (which does not included EM effects), we MUST use lumped ideal components as an approximation. Why do you keep coming back to this? One more time. Circuit theory does not include EM effects. TLs can only be analyzed using EM theory. To use TLs in circuit theory, we must use ideal lumped components to model them. An open-circuited TL in circuit theory is not equivalent to a (ideal) capacitor - period - case closed. If you want to model a physical capacitor in circuit theory, then by all means, add ideal components to your hearts' content until it works like you want as long as you keep in mind, there are no EM effects in circuit theory. Alfred Centauri 01:24, 20 September 2005 (UTC)
I just perused the links and what I see in these papers is that the physical capacitors referred to in the papers are modeled with cascaded lumped IDEAL elements including - you guessed it - capacitors. So, they are modeling a physical capacitor with capacitors (and other lumped elements). Doesn't that sound circular? Not to me. They are using IDEAL lumped elements to model the physical TL related effects. Alfred Centauri 02:52, 20 September 2005 (UTC)
Look at Figure 1(a) of the paper CAPpesc.pdf that you linked to. That looks a lot like our contrafeed thing doesn't it? Alfred Centauri 03:20, 20 September 2005 (UTC)
-- Light current 08:07, 18 September 2005 (UTC)
a) OK, identically constructed devices behave identically
b) OK, physical capacitors, like all physical components, exhibit TL related effects. BTW, have you considered the TL formed by the leads connecting the source to the cap?
c) I'm still working on performing this experiment on campus with some of the 'old' EM lab gear. I've also asked others to look at my 'analysis' of this thing. Alfred Centauri 01:31, 20 September 2005 (UTC)
moved to talk transmission line
Imagine an ideal current source connected across an empty (discharged) vacuum dielectric capacitor. Turn on the current source which acts as a pump for electric charge. The current source will merrily pump charge from the bottom plate to the top plate (say) and the voltage across the capacitor will ramp up. In this scenario, there are a couple of interesting questions.
1. Is any charge current actually passing between the plates.
2. Does anything pass or need to pass between the plates to allow the capacitor to charge? If so, what is it? -- Light current 15:08, 19 September 2005 (UTC)
No I meant is there anything passing directly between the plates via the dielectric? If so, what?
The information that there is charge build up on one of the plates is communicated to the other plate by the electrostatic repulsion of similar charge carriers in the other plate. So they get pushed down the wire. Yes?? So what passes between the plates is information in the electric field?-- Light current 03:17, 20 September 2005 (UTC)
Exactly, O, but what AC and I are trying to establish here is the necessity (or not) of displacement current in capacitors. He say YO! (probably), I say -- dont know!. So we're just working thro the argument step by step. Any insights you have along the way would be interesting.-- Light current 12:25, 20 September 2005 (UTC)
Are you trying to say that the magnetic field, if it existed in the (open circuit from a low freq POV) system would then collapse?
Im going to think about this very carefully before I answer.-- Light current 15:03, 20 September 2005 (UTC)
Let me get you straight. Are you saying that as each new 'electron' or packet of charge reaches the top plate, then the electric field between the plates jumps up a bit? Is so I would agree. Is this your sudden change in electric field?-- Light current 15:21, 20 September 2005 (UTC)
I think I see what you may be getting at. As the charge difference builds up on the plates, an increasing electric field is produced between them. According to old J.C. Maxwell, a changing electric field here produces a magnetic field that is propagated into space at the speed of light outward from the capacitor plates and with the changing electric field you get some EM radiation.(traveling magnetic waves cannot exist alone - can they?) Now I think E x H gives the direction of the radiation and this would appear to be radial from an axis perpendicularly joining the centres of the capacitor plates, Yes? So nothing is actually passing between the plates yet then?
But heres an interesting thought: Assume that this radiation is indeed radial and assume we have a circular parallel plate capacitor. Also assume that this radiation starts from the centre of the capacitor (where else could it start?) When the travelling EM wave reaches the periphery of the capacitor discs it sees an *open circuit* so what happens to it? ;-)-- Light current 15:46, 21 September 2005 (UTC)
Let me try to offer some suggestions here. It seems you are having trouble because your second differetial of E is zero. Right? However, the charge flow cannot start infinitely slowly. Neither can it end infinitely slowly. So there will be a non zero 2nd diffl at the the start and end of the charging period, does that help at all?-- Light current 22:43, 26 September 2005 (UTC)
Yes, I understand what you are trying to do now. THe radiation maybe constant but IMHO it cant escape the interior of the capacitor because it sees an o/c at the ends. Do you agree with me on that one?-- Light current 23:21, 26 September 2005 (UTC)
Just a simple question here. Are you both sure that charges in the wire or on the plates come to rest very quickly? Or do they slow down gradually as they meet more of thier friends? (electr static repulsion). I suggest that the only thing going fast here is the EM energy (parallel to the plates of the capacitor). It travels at the speed of light in the medium. There is minimal effect due to charges decelerating because they're not travelling very fast in the first instance!-- Light current 00:46, 5 October 2005 (UTC)
No. The whole point of this discussion is to show (hopefully) that no charge needs to move to get EM radiation. That this is so only requires consideration of EM propagation in vacuo.-- Light current 01:24, 5 October 2005 (UTC)
Also, I can't see how you can get very high time rates of change of charge density if you dont have the actual charges moving at the same high rates (even at the (sub)atomic scale). I also notice that you have sneaked the concept of displacement current back into the argument. This has not been proven to exist. In short, I think there is no cat up your tree!(Woof! Woof!) [3]-- Light current 01:36, 5 October 2005 (UTC)
If charge cannot move at 'c', what is your mechanism for the actual charge density wave to propagate at 'c'. You are trying to find a mechanism for how ordinary current (the slow movement of charge carriers) converts into EM radiation. It cannot directly be due to the acceleration of the charge carriers as has been calculated by Pfalsted. Therefore there must be another process. (Unless of course the EM energy is already there in another guise, like dc? Refer to my original question about diff between EM and dc)-- Light current 15:07, 5 October 2005 (UTC)
You definitely need movement of charge to get radiation. Pfalstad
Where does this moving 'charge' come from in a vacuum borne EM wave? Are you just talking about the initial generation of that wave in a conductor system? Propagation of Electromagnetic waves doesnt involve charges moving does it?. If you are talking about the generation of EM waves in an aerial system, this seems to be what AC is talking about (as far as I can tell) and this seems to be what AC is trying to work out. i, on the other hand, do not offer any explanation of How charge current is converted to EM radiation. My suggestion is that the EM radiatiopn and actual charge current are (almost totally) independent of each other. Take a battery, and a parallel pair of wires connecting the terminals to a load resistor via a switch. We know that the energy travels at'c' but the charges travel much more slowly. You will probably say: Ah yes-- but the charge density wave travels at 'c'.In that case, I must repeat my earlier question which was: what is your mechanism for describing light speed travel of charge density? Or to put it another way, what is it actually that travels at light speed to cause these fluctuations in the charge density on the wire. The answer of course can be only one thing: EM radiation flowing between the wires (not in them) -- Light current 21:25, 5 October 2005 (UTC)
Ah.my dear Pfalstad. Yes. I agree with the above post of yours. What Ive been trying to explian to Alfred (not very sucessfully) is that it is the EM wave that is fundamental and the current, mag field etc are all a result of that. I suppose you could say that the EM wave drags along the charges as fast as they will go. When a capacitor is charging slowly is when I have a slight problem because I cant see the mechanism by which 1 electron per half hour say arriving at the top plate can give rise to all the effects that Alfred seeks especially when you have both almost agreed that the electron deceleration can give only a tiny amount of radiated power. The only possible solution I can see is that each electron, as it arrives, is accompanied by a tiny amount of EM radiation (which has actually dragged it along). This radiation flows into the top plate and sets up a standing wave of very small amplitude travelling from one end of the plates to the other end and back again.. As more and more electrons arrive,(againg accompnied by their associated EM energy) the standing wave amplitude in the capacitor slowly builds (in a linear manner if current fed). Of course, if the EM adds non coherently (out of phase) in the transmission line between the capacitor plates, the voltage produced across the plates will show some noise (if you had anything sensistive enough to see it).I'm not sure whether it does or not. I would be interested to know what you think of this suggestion.-- Light current 23:57, 5 October 2005 (UTC)
Please dont call my ideas ludicrous. If you think they are wrong, disprove them. My previous statement about charges being dragged along was very sloppy (made without due thought)and I retract it. The charges in the conductors are induced in the surface of the conductors and therefore dont need to move along the wire in the direction of the energy vector. So do charges play any part in energy transfer at all? If you are preparerd to listen to my arguments without trying to score points or deride my attemts at explanation, imply I'm a crank etc, I will be happy to try to explain my viewpoint. Whether you or others agree is up to you/them. But if not, it will be incumbent upon those persons to demolish my arguments one by one not just try to dismiss them as cranky thoughts-- Light current 19:26, 8 October 2005 (UTC)
moved to talk:transmission line
Im not going to go as far as saying an electron is ONLY an EM wave. As we have established earlier, it seems no one knows exactly of what an electron consists. However, certain of its attributes may be explainable in terms of EM waves.-- Light current 16:53, 13 October 2005 (UTC)
We still have something of a paradox here. We know for instance in a real TL travelling waves produce losses due to skin effect, but in a situation we have just described, we find zero or very low losses. Can you say why?.
Well I say my model is correct. The reason there are no losses is that there is no net current. This therefore lines up with the actual situation of a charged TL.-- Light current 03:15, 13 October 2005 (UTC)
However, the importance of this apparent duality of EM waves and steady dc, in my mind, cannot be underestimated. It should have impressed you also, although you seem remarkably blase about it!. If the duality is accepted, it has far reaching consequences on the nature of those things we call voltage and current. I will leave the idea with you a little longer before suggesting applications and ramifications of this duality idea.-- Light current 17:47, 12 October 2005 (UTC)
BTW, if you had been taught this idea at university, college, would you have believed it?-- Light current 18:11, 12 October 2005 (UTC)
Sorry, I thought I had described what the point was. Obviously you do not wish to accept the implications.-- Light current 01:57, 13 October 2005 (UTC)
OK heres one. Is a simple battery a source of dc only, or is it also a source of EM radiation. Please think crefully before answering! ;-)-- Light current 17:10, 13 October 2005 (UTC)
Heres some more thoughts. What function do the charges on the transmission line conductors have in the transmission of the EM energy back and forth in the line. Do they need to be mobile carriers? Do they need to move?. Do they need to be there at all.? I think I can answer these questions, but I leave it to you or AC to comment first -- Light current 17:37, 13 October 2005 (UTC)
Of course, one would normally say that a battery is not a source of EM radiation at all. However if steady dc can be represented as counter propagating waves then one must ask the question. THe reasons you give for the necessity of mobile charge carriers in the TL are not logical. For instance, its possible to have charge separation in a dilectric is it not? Im not saying electrons dont exist! Your last sentence, maybe, highlights the difficulty with the idea: ie if these waves cannot be distinguished from steady dc, what does that mean?
There are a few conclusions one could draw.
a) a transverse electrostatic field in a TL CAN be generated by an initial one way flow of energy as when charging, and then maintained by the counter propagating EM waves. (showing some equivalence between EM and dc.)
OR b)travelling EM waves do not exist in the TL at any time. So how does the energy get there?
OR c) travelling waves are initially used to charge the capacitor but when charged, the waves stop moving suddenly. But how do they do that? ie what is the exact mechanism by which they are stopped- and stopped instantaneously at that?
AS I said before, things that cannot be distinguished as different my any method whatsoever might as well be considered the same. Whether they are truly the same or not is a philosophical question, not one of physics.-- Light current 17:17, 16 October 2005 (UTC)
Could you say what you mean by that in plain English please?-- Light current 01:53, 13 October 2005 (UTC)
The fields we are considering are not in free space, the electric field exists between the two conductors. I didnt say anything about the charge densities on the conductors. AC I dont think your above statement says a great deal. We have a steady (dc) electric field. But we also have two counter propagting ac waves that have been show to add up to the dc version. Does this worry you at all?-- Light current 16:17, 13 October 2005 (UTC)
You haven't shown anything as far as I am concerned. You have made some hand-waving arguments that aren't very good and you believe that you to have shown something? Do you consider this rigorous? Please show mathematically what you claim to be shown. Do you agree that the electric field between the conductors of the charged TL is due to the net electric charge on the conductors? The conservative part of the electric field is, by Gauss's law, due to electric charge. The non-conservative part of the field is due to changing magnetic flux. Potential difference (voltage) has meaning only for a conservative field. The voltage across the conductors of the charged TL must be due to a conservative field. This field can only be created by electric charge. Alfred Centauri 17:44, 13 October 2005 (UTC)
I am trying to find a way of explianing this waveform thing mathematically using Heaviside functions. But I need to do some research first.-- Light current 21:43, 15 October 2005 (UTC)
Since this aspect seems to be causing a lot of controversy with regard to the validity of my arguments on the transmission line circuit, I am going to try to answer all the points opn this aspect that have been made. To do this I must go back and review all the posts (mainly from AC) so I know exaactly what the objections and comments are. I therefore hope that AC and other interseted perties will bear with me whilst I do this revision and compose a reply. Thank you for your patience.-- Light current 01:30, 14 October 2005 (UTC)
By studying some of your earlier posts on the generator problem AC, Maybe I can cut short the discourse by saying the following:
Let the generator remain connected for all time after the initial connection. At the time of arrival of the reflected wave front, there is 2V from the gen, and 2V on the line. Now what is the current thro Rs (the generator source resistance)? Zero!. So from the point of view of the wave, what impedance does it see? Infinity. So what does that mean? Is it a short, open or matched?
The resistance of a resistor is still the same if its in the drawer, but that doesnt mean it has any effect. Think of bootstrapping. Actually, come to think of it, it doesnt really matter what the impedance is after the lines charged as long as the gens still connected. It could be zero, 50ohms of infinity as far as the signal is concerned. Thats because no current can flow thro this resitor. So it can be defined as anything you like. But its not connected to ground - its connected to 2V. The wave incident at this resistor cant push any current thro it. (cos theres 2V on the other side. The wave couldnt push any current thro an o/c if that was there instead could it?. So as far as the wave's concerned, it might as well be an o/c. Also, this must be true, otherwise the wave would pass current thro the resistor and the reflection would be less than it actually is. THat would mean there would not be 2V on the line after 2T. Can you see it now? I dont think there are many other ways to explain it. T
The standard way of testing the impedance is to look at the reflected signal. rho = (Zl-Zo)/(Zo+Zl) where rho is the reflection coefficient.(reflected ampl /incident ampl), Zl is the load resistor. In our case, rho=+1 (all refelected with no inversion), yes?- so you can work out Zl for yourself.-- Light current 06:36, 16 October 2005 (UTC)
No. The applet is completely correct. Thats what I ve been saying all this time. THe applet shows the total voltage on the line which is made up up of the sum of each traveling wave. (V+V=2V). I shows the two travleing waves add to give dc! BTW a TL can have a waves travelling in both diections simultaneously but Im sure you knew that.-- Light current 19:07, 16 October 2005 (UTC)
I know thats the way you prefer, but its not correct because energy is still flowing behind the wave front. That this is so can be seen because until the reflected wave reaches the near end again, energy is still being pumped in to the line from the generator and all waves are travelling!-- Light current 21:09, 16 October 2005 (UTC)
If you were taught that the 'Changing part' or any other part of the wave is absorbed by the teremination, I think that is definitely wrong or you may have misunderstood it. How can the termination absorb energy? (I^2*R*t) - there's no current in it (as I have said before!) Once the line's charged, yes the energy input into the line stops, but the waves inside the line carry on traveling. If they dont, can you describe how they are stopped?-- Light current 21:50, 16 October 2005 (UTC)
If you dont know how the waves are stopped, why not just say so. I dont know how they can be stopped either. But its just possible that they are in fact stopped and we have discovered something new! -- Light current 22:00, 16 October 2005 (UTC)
But a resistor would only absorb some energy, not stop the waves. Then we would be short of energy on the line. This does not happen in the real case. EM waves can be generated and absorbed. THey cannot be stopped! What does a stopped EM wave imply? It cannot be sustained. It must travel to live!-- Light current 22:24, 16 October 2005 (UTC)
If the length of the resistor is troublesome, imagine instead a current source with a parallel matching disc resistor of infinitesimal thickness connected actually in the coax line from inner to outer. In this case of course, the current source would need to keep pumping to provide the essential mismatch at the near end. I repeat that the resistor cannot absorb the wave. If it did, it would absorb all the energy that we had just put into the line, and the line would never charge up. Just have a think about it a while. Also, if the edge reaching the near end after reflection is not perfectly square, the generator merely turns off a bit more slowly to correct the situation. Its a bit like unity feedback in a way.
If you dont accept the basic argument, I dont see what difference a load of math (necessarily based on the same argument) will make. Nevertheless, if I do come up with an alternative explanation you will see it here.-- Light current 03:07, 17 October 2005 (UTC)
OK just one last try on the qualitative argument. THe voltage source with internal resistance Zo is left connected to the line for all time.
Lets assume you are correct in that the source resistance does indeed absorb the refelected wave. But if you allow that, you must accept that it absorbs all of the reflected travelling wave from the line, not just some of it. OK? Right, now in this way of looking at it, the generator continues to send energy down the line for ever and a day, but absorbs this energy after its round trip when it gets back. The line is fully charged and cant accept any more energy. In this way of looking at it, the line is still fully charged, waves are counter propagting up and down the line, and the line is terminated in its characteristic impedance. Happy?-- Light current 03:30, 17 October 2005 (UTC)
If I have missed an important part of your argument, please let me know and I'll go back and look again at your earlier posts on this aspect.-- Light current 02:14, 14 October 2005 (UTC)
Thank you for your courtesy in replying swiftly to my last post. It will save me a great deal of work in preparing answers. I have enjoyed this discussion, and I'm sorry I couldn't convince you of my ideas. We will therfore have to agree to disagree! If I can think of a mathematical proof I will surely publish it here-- but dont hold your breath!-- Light current 04:40, 14 October 2005 (UTC)
If you consider pulse charging of this capacitor, you will see that the traveling waves do indeed add up to dc. Get a battery and a capacitor. Connect them, then measure the capacitor voltage. Its dc! But EM waves have been used to put the energy there.-- Light current 18:01, 8 October 2005 (UTC)
How do the EM fields become established then if not by EM waves?-- Light current 20:49, 8 October 2005 (UTC)
Just another thought. A battery charging a capacitor transfers energy to the capacitor. Right? How does the energy travel from the battery to the capacitor? (Not thro the wires)-- Light current 19:12, 8 October 2005 (UTC)
Im not sure to which idea of mine you (AC) are specifically referring. Is it the one about energy flowing in the space between the wires or the fact that EM radiation is more fundamental than current?. Any way I thought you were having a Wikibreak! -- Light current 01:36, 6 October 2005 (UTC)
I keep telling you - I'm not a physicist!-- Light current 00:36, 6 October 2005 (UTC)
I'm not trying to tell you anything. I am putting forward some ideas which I believe have some merit for discussion. (BTW I was trying to move the argument forwards with Pfalsted in the understanding that you had temporaily retired from the ring). Yes I admit that communication has been difficult between us. Thats probably because your EM theory etc is far in advance of mine. I have to rely on my meagre (and outdated) knowledge and some common sense. The standard argumnets relating to capcitors charging and the details of EM radiation, how charge is carried by an electron etc do not satisfy me. I'm sure they dont satisfy you either. I am not trying to yank your chain as you put it but to try to develop my (albeit far less than perfect) thoughts on these matters with the help of yourself and others of superior intellect to mine. You mustn't expect everyone to be as smart as you are! THats it Im clean now!-- Light current 01:58, 6 October 2005 (UTC)
OK, AC. I understand that you are not considering displacement current at the moment, but EM radiation due to accelerated charges (which is virtually nil- we think). So that leaves the tricky question of what actually passes between the plates of the capcitor if its not radiation.
BTW If you do decide to consider 'displacement current' in the future, could you please say whether its the sort that Maxwell defined, or the sort that is supposed to accompany propagating EM waves. I think this will save much confusion. THank you!-- Light current 22:07, 5 October 2005 (UTC)
Moved discussion to Wikipedia Talk:WikiProject Electronics
It says the main reason for using oil in old large capacitors and transformers is because of the heat generated. Funny, I thought it was used mainly as an insulating medium and dielectric.-- Light current 02:38, 20 September 2005 (UTC)
OK, its for cooling as well!-- Light current 03:23, 20 September 2005 (UTC)
But not mainly for cooling in capacitors as they shouldnt get very hot (unless thers a lot of ripple current and a high ESR). So I intend to correct this statement.-- Light current 14:33, 20 September 2005 (UTC)
Ive posted a dispute tag in this area, because I dont believe in general that oil is used for capacitor cooling. Quote from manufacturer literature:
'# Why are GAEP high voltage capacitors oil-filled?
Highly insulating oil is used to suppress partial discharges (corona), increase the dielectric strength, and increase the effective permittivity (dielectric constant) of the capacitor dielectric. Oil-filled film capacitors have high energy density in comparison with other types of capacitors used at high voltage, such as ceramic capacitors. Different types of oils are used with different types of capacitor dielectric and electrode designs. '
-- Light current 00:37, 26 September 2005 (UTC)
Remember the oil filled transformers that contain the special transformer oil and the large theory associated with it. -- Davy Jones 01:19, 11 October 2005 (UTC)
Pardon?-- Light current 15:48, 11 October 2005 (UTC)
Why? This page is about capacitors.-- Light current 01:53, 12 October 2005 (UTC)
This is another new one on me. I didnt know that low ESR was essential for integrator capacitors. Did the author really mean leakage current? I think he did, but Im willing to be persuaded otherwise.-- Light current 22:05, 3 October 2005 (UTC)
I would suggest that the effect of capacitor ESR in integrators is minimal. THe leads you use to connect the capacitor have probably got more resistance than a half decent caps ESR (0.0001 ohm say)-- Light current 23:27, 3 October 2005 (UTC)
Just looking at manufacturers websites. Low ESR caps are about 0.01 ohm (10milliohm). So I was only 2 orders of magnitude out.!! ESR seems to go down with increasing frequency. Not sure why.-- Light current 22:20, 8 October 2005 (UTC)
Whats the resistance of 1" of 1oz copper PCB track say 10 thou wide? (in milliohms).-- Light current 23:39, 13 October 2005 (UTC)
I think this page is getting near to being good enough to be considered as a featured article. But is it too long for that. Any comments?-- Light current 14:40, 5 October 2005 (UTC)
Well Davy Jones, (un?)fortunately, this sort of stuff is not accepted by the community at large and is considerd new research!. As such it cant really be incorporated into WP articles. My purpose here on Talk is to try to get editors thinking critically in order to sharpen up their skills for the purpose of creating great, accurate and easy to understand articles.-- Light current 18:17, 12 October 2005 (UTC)
Since I have now started the long awaited (by some) page on Ivor Catt, I wonder if we should move all the discussions about Catt related subjects on this page to Talk:Ivor Catt. Could we have some comments please ASAP-- Light current 14:05, 15 October 2005 (UTC)
OK I'll just wait for one or two agreements from our project team before proceeding!-- Light current 21:31, 15 October 2005 (UTC)
Do we need these pictures her or would they be better on the practical capacitors page? -- Light current 01:25, 22 November 2005 (UTC)
In capacitors when newly electrons (of charge -Q) approaches one plate it will experience of force of repullsion from the negatively charged plate, and this increases their potential energy and the potential across the capacitor will increase But as -Q approaches, -Q from the opp plate will get repelled (inducing a +Q on the plate),
The question now if this is happened shouldnt the potential of the capacitor becomes constant because as ΔPE comes from -Q on one plate shouldnt ΔPE is lost (or transferred) from the opp plate
-- Ducky12345 ( talk) 16:19, 2 March 2008 (UTC)
The information isn't trivia, rather, it shows how the layperson may conceptualize the use of the word. Zaphraud ( talk) 20:03, 21 October 2008 (UTC)
Ccrrccrr ( talk) 12:08, 24 October 2008 (UTC)
When I'm logged in the images show up in the right place, but when logged out the images appear ontop of the text like in this screen shot of Capacitor. There are blank spots in the text where the images are supposed to appear further down the page. This is with Firefox 2.0 on osx. Autopilot ( talk) 01:39, 24 November 2008 (UTC)
This article is the WP:WikiProject Electronics collaboration for December 2008 to January 2009. Please suggest and claim responsibility for improvements here. Please don't use this section to discuss improvements, so new editors can easily participate. Potatoswatter ( talk) 23:57, 14 December 2008 (UTC)
Rename "filtering" section to reflect exclusion of signal filtering. - [anon]
I'll take on the unideal bahaviour section if that's ok with everyone. SpinningSpark 00:30, 15 December 2008 (UTC)
<- As I said, I'm quite neutral about this. The consensus in textbooks and in this discussion lies with the charge integral, so let's stick with that. I only intended this to be a brief talking point and it's probably time to move on to something else! Papa November ( talk) 14:20, 20 December 2008 (UTC)
This article starts with "a capacitor... is a passive electrical component". That's much too narrow a definition for an article that is simply called "capacitor": it is simply any pair of conductors separated by a dielectric. The article then focuses entirely upon man-made capacitors, and their applications in Electronics. We could expand and rewrite the article to include natural capacitors, and avoiding putting undue weight on man-made devices.
Alternatively, we could do the following:
Opinions? Papa November ( talk) 15:29, 20 December 2008 (UTC)
Sections for topics that are tangential here and already covered in other articles, like displacement current, we should possibly move to capacitor/deprecated sections. Potatoswatter ( talk) 04:35, 22 December 2008 (UTC)
I mostly recall seeing in textbooks but permittivity and this article use . Which do we prefer? I vote for the one which isn't a "variable" but I'm not really informed in these matters. Potatoswatter ( talk) 02:21, 21 December 2008 (UTC)
The main article for microphony as an undesirable effect is microphonics (although it is not a very substantial article). Condenser microphone is certainly the same physical effect but is not really in the context of non-ideal. Do you want that changed? SpinningSpark 12:20, 21 December 2008 (UTC)
There's a whole mess of other articles about capacitors. (Guess they're pretty sexy.) I think it would be a good idea to keep our eyes open and make sure they're all in the category. A number of them should be merged into electrolytic capacitor. Potatoswatter ( talk) 04:08, 22 December 2008 (UTC)
Uh, "The common parallel plate model reduces such a capacitor to a one-dimensional cross section." I know nothing about capacitors, but wouldn't two broad plates separated by a small distance be commonly modeled in two dimensions? (heck, the picture uses three). If the sentence is truly about a one-dimensional mathematical model, wouldn't it be better placed well before the intro of the concept of parallel plates? — Joel D. Reid ( talk) 04:23, 27 December 2008 (UTC)
Would the other editors taking part in this collaboration be agreeable to putting this article up for GA review. I don't have a great deal of experience of this, but when I have been through it before the main things are that [1] you keep monitoring the review as it progresses so that problems are dealt with in a timely manner (otherwise the reviewer loses interest and goes away) and [2] absolutely everything has to be referenced, ie every para. If you are all prepared to work on the article at this level I propose putting it up.
Also, I think the ESR section needs some work, the maths looks gastly. A diagram would help to simplify it. I will work on that bit if there are no objections. SpinningSpark 20:51, 5 January 2009 (UTC)
"Capacitors were discovered in glass jars in 1745 . . ."? How about "The first form of capacitor was the Leyden jar, invented in 1745 . . ." -- Chetvorno TALK 15:55, 29 January 2009 (UTC)
Friends, i am a HT consumer in india. in our montly billing our power factor is only 0.89. it has been advised by the electricity board people to add capacitors in our circuit. i wish to kno how the rating of the capacitor is arrived at and also how this has to be connected in the circuit.i heard that extra precautions need to be taken while switching on the Generator. i heard while switching on the circuit the capacitor needs to be disconnected.please throw some light on this. —Preceding unsigned comment added by 59.90.213.170 ( talk) 13:16, 11 March 2009 (UTC)
In looking through electronic catalogs, I see that certain electrolytic capacitors are referred to as “Snap-In” capacitors, but I do not know what that means. Does it refer to a socket type - or what? An explanation would be appropriate for this article. I am sure that some thought could be give to expand this article to include definitions for many of the jargon words pertaining to capacitors. Stan ( talk) 18:00, 13 April 2009 (UTC)
In the last section:
Capacitors used in RF or sustained high-current applications can overheat,
What does RF stand for? A quick google search didn't turn up something useful. Perhaps someone can add it to the article. Thanks Panoramix303 ( talk) 22:24, 22 May 2009 (UTC)
Radio frequency. SpinningSpark 23:12, 22 May 2009 (UTC)
wat's difference between polarised and non-polarised capacitors and their functions? —Preceding unsigned comment added by 115.99.0.27 ( talk) 08:48, 29 June 2009 (UTC)
I made a photo of a variable capacitor made of 2 wires near each other in a frame:
At least that's what I think this is supposed to be. Not sure, if another picture of a cap improves these articles, but this one clearly shows the "inside" of a cap. You may add it to the articles Capacitor, Types_of_capacitor and/or Variable_capacitor.
Should I trim the irrelevant stuff from this image?
I am an educated person, though not in physics. (I took undergrad courses in physics & calculus ~15 years ago, but my PhD is in nutrition.)
I am now training as a volunteer at a large science museum where I live. I will be conducting demonstrations for tour and family groups (mostly kids), including a demonstration on static electricity. Part of the demonstration uses Leyden jars. In my search for more information about how Leyden jars work, I have been frustrated by technical articles describing ratios of charge to potential differences and such when what I really wanted to know was where the electrons went and how the charge was changed on the outer plate in response to the inner plate. Does the outer plate have to be grounded to allow the opposite charge to accumulate? Or is it a partial charge resulting from electron movement within the plate itself? What determines the voltage of an arc caused by touching the pole? Is it a simple matter of how many electrons are stored in one plate or the other? (I'm not looking for these answers on this talk page, just listing the kinds of questions I wanted to learn about in the article but had difficulty with. No need to respond directly to these questions here on the talk page.)
I just want you knowledgeable and talented physics and math people to know that this one guy (me) had a really difficult time learning what I wanted to know from this page, and I want to ask you all to consider presenting information here in a manner that might be more understandable to people like me who aren't that strong on our physics or calculus. I think a kid working on a transistor radio in shop class should be able to take away at least basic knowledge of how capacitors function. I appreciate the fact that all of this technical information is here for anyone who wants to learn the details, but please consider writing a basic description of the principles with us laypeople in mind -- maybe in its own section.
But please don't think of this as a harsh criticism. I truly do appreciate the work you've all done to bring an enormous amount of information to the Wikipedia knowledge base! Someday I might want to brush up on my physics & learn this stuff properly. Dcs002 ( talk) 01:01, 10 October 2009 (UTC)