AC flowing through a cap. What actually happens?

[BrownOut]

I deny that "we" don't care what Maxwell said anymore. You seem to pretend to speak for other people, but I don’t' see any evidence that others feel that way. Why is it do you think so many lectures and so much is written in textbooks about Maxwell's equations, and displacement current, if people don't care about it. Sad for you, but "we" care about what Maxwell said very much. I also deny that anything has changed since Maxwell's days. Physics doesn't change, and aside from a minor point about ether, everything Maxwell wrote is true today as it was 150 years ago. I also deny that anyone has proven Maxwell wrong. Further, I see no evidence that eggs, bowling balls, 2X4's or any other irrelevant analogy has anything to do with what we're discussing. And I see no reason to believe that repeating unsubstantiated claims that displacement current doesn't flow between the plates of the air capacitor over and over and over. Clearly I'm not impressed by a bunch of kindergarten-level demonstrations, false analogies, circular logic, etc. I'll continue to side with Maxell over Sesame Street. As for "some other" evidence, I'm linked videos of university lectures, textbook excerpts, I've show the equations, I've presented logical arguments that shows without ambiguity why this is real, shown the untis are consistant and shown the identities are consistant with the other laws of physics. All of which has been ingored. No amount of evidence I show will ever be enough, so there is no point for me putting in more effort. I've presented a solid case, but some continue to catagorically deny it. I can't do anything for those folks. Lastly, I know about the times Maxwell lived in, so no need to council me on what to read up on.

 

[Jony130]

The simple concept of a current being charge carriers flowing in a conductor or in a beam (eg. in a CRT) has served us well for 200 years but it MAY need to be revised.

Well in "Standard Handbook for Electrical Engineers" we can read:
”Metals are conductors for current, but nonconductors for the flow of energy, while dielectrics are good conductors for the flow of energy.
A significant point about this phenomenon is the fact that electromagnetic energy flows predominantly through dielectrics (non conductors). Metals are conductors for current but nonconductors for the flow of energy, while dielectrics are good conductors for the flow of energy.
Near the surface of a transmission line conductor, the Poynting vector is slightly inclined towards the conductor's surface, thus giving rise to a small component of energy flow into the conductor. This component of the electromgnetic wave causes the conductor current, which in turn causes a loss but does NOT contribute usefully to the power transmission.
The usually accepted view that the conductor current produces the magnetic field surrounding it must be displaced by the more appropriate one that the electromagnetic field surrounding the conductor produces, through a small drain on its energy supply, the current in the conductor. Although the value of the latter (the conductor current) may be used in computing the transmitted energy, one should clearly recognise that physically this current produces only a loss and in NO WAY has a direct part in the phenomenon of power transmission.”

 

[BrownOut]

That's fascinating. One might even say that the component of the Pointing vector that is directed into the wire displaces the conduction current along the wire.

 

[Ratchit]

MrAl,

I hope i've made this all clear but if you have any more comments please feel free to note them here even if you dont agree with something here.

Quite a presentation, but I prefer something more basic. First of all, current is not a concept. It is a defined quantity of moving charge carriers. If you think of it as a concept, then every quantity would be a concept, and the word would have no meaning. Charges like to flow along conduction paths. What is really fundamental is that current will exist through a component if a conduction path exists through it (like in resistors and inductors), but not if no path exists (capacitor). One can measure a current on both sides of a capacitor and conclude that charge is flowing through the capacitor. But in reality, charge only appears to flow through the capacitor. The dielectric (especially a vacuum) stops the charge flow cold, and charges can only accumulate, deplete, and separate on the plates. As an example, one can measure simultaneously the current in the primary and secondary of a transformer, and conclude that some current is transferring from the primary to the secondary. But we all know that the primary and secondary are really isolated.

As far as I can determine, displacement current is pretend, apparent, artificial, mathematical, and not real. It is an equivalance to the changing electromagnetic fields that occur within a capacitor when its energy storage level (voltage or charge imbalance) is changing. That is why it mirrors the external current. The fact that Maxwell used that concept (a field to current equivalance) to predict electromagnetic radiation does not change that fact. I know of no reason to worry about displacement current except when studying the internals of a capacitor with respect to Maxwell's equations. Circuit analysis from a macro viewpoint seems to get along just fine by defining the external characteristics of a capacitor as a storage element.

Hopefully, the professor will show up soon to set us all straight.

Jony130,

Well in "Standard Handbook for Electrical Engineers" we can read:
”Metals are conductors for current, but nonconductors for the flow of energy, while dielectrics are good conductors for the flow of energy.

Energy is transferred anytime charge carriers move, whether by conductors or dielectrics. A resistor connected by low resistance wires to a voltage source will demonstrate that those conductors do a good job of transferring electrical energy. Much better than a string of capacitors (dielectrics) connecting the resistor to its voltage source.

Ratch

 

[BrownOut]

I guess the question should be asked: Are there any other identities in physics, with consistant units of measurement and with consistancy with other physical laws that aren't real?

 

[MrAl]

MrAl,



Quite a presentation, but I prefer something more basic. First of all, current is not a concept. It is a defined quantity of moving charge carriers. If you think of it as a concept, then every quantity would be a concept, and the word would have no meaning. Charges like to flow along conduction paths. What is really fundamental is that current will exist through a component if a conduction path exists through it (like in resistors and inductors), but not if no path exists (capacitor). One can measure a current on both sides of a capacitor and conclude that charge is flowing through the capacitor. But in reality, charge only appears to flow through the capacitor. The dielectric (especially a vacuum) stops the charge flow cold, and charges can only accumulate, deplete, and separate on the plates. As an example, one can measure simultaneously the current in the primary and secondary of a transformer, and conclude that some current is transferring from the primary to the secondary. But we all know that the primary and secondary are really isolated.

As far as I can determine, displacement current is pretend, apparent, artificial, mathematical, and not real. It is an equivalance to the changing electromagnetic fields that occur within a capacitor when its energy storage level (voltage or charge imbalance) is changing. That is why it mirrors the external current. The fact that Maxwell used that concept (a field to current equivalance) to predict electromagnetic radiation does not change that fact. I know of no reason to worry about displacement current except when studying the internals of a capacitor with respect to Maxwell's equations. Circuit analysis from a macro viewpoint seems to get along just fine by defining the external characteristics of a capacitor as a storage element.

Hopefully, the professor will show up soon to set us all straight.

Jony130,



Energy is transferred anytime charge carriers move, whether by conductors or dielectrics. A resistor connected by low resistance wires to a voltage source will demonstrate that those conductors do a good job of transferring electrical energy. Much better than a string of capacitors (dielectrics) connecting the resistor to its voltage source.

Ratch

Hello again,

Ratch:
Well from reading that im not sure if you are agreeing with me or disagreeing. You seem to be stating something that i illustrated as if it is not what i said
I cant see how you gleaned "current is not a concept" from moving eggs, which clearly represented electrons.
I also mentioned that this was not going to be a perfect analogy, and the analogy itself represents an interpretation of Maxwell.
Yes it appears that Professor Viken has a life, unlike many of us who insist are arguing about things that matter little to us anyway as Mr RB pointed out several times I do hope he makes it back soon though. We'll just have to wait until his schedule permits, that's all. His academic schedule is not 8:30 to 5, 7 days a week.

Brownout:
Again with your complaints you have again contributed nothing new to the thread. I already know you dont agree with anything some of us have posted and you cant accept analogies for anything other than what you say is ok to accept. Just to let you know, you havent changed my view on anything since day 1 and apparently you are never going to. From the childish way you act here in this thread (from your comments) if you said later today that the sun would again come up in the morning tomorrow as usual, i'd be pretty darned scared and start saying my prayers because i would tend to believe that it wasnt really going to come up tomorrow solely because you said it would! So you see by responding that way you really dont do yourself justice.

Jony:
I believe that is the "total field" view which i think is in vogue presently, ie the field is responsible for everything. One of my first comments when i joined this thread was "Everything is an abstraction of reality". That basically means when we go through the process of understanding something, we have to pretend to understand to a certain point and use a host of abstractions to try to understand it. To put it another way, "We have too much information" and not enough reality".
And as far as communicating these abstractions to other humans, i believe it was Feynman who pointed out that "my abstractions are not the same as your abstractions".

 

[BrownOut]

Mr. Al. What complaints? Is anyone else crying about my complaints? I don't see where you're contributing anything new to the thread either, so before you cast aspersions on someone else, look at yourself. Most of us who are engaged in this discussion took electrical engineering in college, and get nothing from your simplistic analogies. I really don't care if I change your mind or not. Nothing will, so that isn't a concern of mine. What you think doesn't do me justice is also a non-concern of mine. You seem to be the only one pouting and having temper-tantrums over what I've written. Sorry if the truth about science hurts your feeling so, but I'm concerned about those who can actually learn something from what I've presented, and so far you seem to be the only one who can't.

 

[MrAl]

Brownout,

Ok then i guess we wont agree on this anytime soon but in some small way i did appreciate your counter points and perhaps in the future we will discover a more common ground again.

Take care,
MrAl

 

[atferrari]

Yes, the rubber membrane...!

Do you remember qtommer? The OP.

His question rang a bell. It was about this explanation coming from the original (longer) articler posted many many years ago Messing Around Activity 2: Capacitors

 

[ljcox]

The leaves in the water tells us that there is something there that is actually happening and something else there that is not only going along for the ride, it's masking the truth behind what is really happening physically. The difference is, in a circuits theory class you might be able to teach that "The leaves are moving and we can see that is true, so that's the answer to what is happening. The leaves move somehow because of their own power".
But in a physics class, you'd want to dig deeper and show that the water is what is really moving the leaves. .
This is essentially my point.

The basic point I was trying to make, is that no one knows what the “Theory of everything” will reveal.

Obviously the theoretical physicists who are at the forefront of physics will have a better idea of where it is going than the rest of us, but I suggest that even they don’t know with any certainty.

 

[MrAl]

Do you remember qtommer? The OP.

His question rang a bell. It was about this explanation coming from the original (longer) articler posted many many years ago Messing Around Activity 2: Capacitors

Hi there,

Oh yes, very nice. I almost forgot about that analogy. I tied to go a little deeper into Maxwells world and the world of electrons to show how electrons might be pictured as Maxwell might have thought about them instead of just the 'flow of water and flexible diaphragm' analogy. Fluid flow is often used for theory, but again it's just theory, and as we should know by now theory is just theory as nothing under the sun explains everything perfectly.
One thing i did not do yet and that is go into the numbers behind the theories. If the numbers dont work out, that's going to look very bad for displacement current theory. Im not sure i want to bother but maybe i'll leave this up to someone else who feels like playing around with the quantities rather than the qualities that we are throwing around in this thread like free pennies
We can talk about the qualities of a matter for ages, but when we start to get quantitative we quickly prove and disprove. We can not beat the numbers. If the little ball doesnt fall into our chosen number on the roulette wheel, we loose. Those few times when it does though it's quite fantastic.

 

[MrAl]

The basic point I was trying to make, is that no one knows what the “Theory of everything” will reveal.

Obviously the theoretical physicists who are at the forefront of physics will have a better idea of where it is going than the rest of us, but I suggest that even they don’t know with any certainty.

Hi,

Oh yes ok. One prominent physicist was quoted as saying, "We will never know why because we can always again ask why".

 

[ljcox]

One thing i did not do yet and that is go into the numbers behind the theories. If the numbers dont work out, that's going to look very bad for displacement current theory.

Brownout & I have both shown that Id = Ic as have at least 2 of the lectures that were posted.

One showed that Ic = 1.2 e^(-t/RC) & Id = 1.2 e^(-t/RC). So what numbers do you need to play with?

 

[MrAl]

Brownout & I have both shown that Id = Ic as have at least 2 of the lectures that were posted.

One showed that Ic = 1.2 e^(-t/RC) & Id = 1.2 e^(-t/RC). So what numbers do you need to play with?

Hi again,

We know that numerically they are equal, but that doesnt prove that they are the same. I can have two eggs in one carton and two eggs in another carton, but the two pairs are not the same eggs even though we count them as being the same. That's the difference between numerical equality and theoretical equality. If the two currents were exactly the same right down to the particle we wouldnt have to call one by a different name.

The numbers i am talking about are to map out atomically what would happen if we say that electrons go into one side of the capacitor and flow through the capacitor and come out the other side, then how do we say that a large quantity of those electrons stayed on the plate (ie accumulated)? For example, we know that the ampere is 1 coulomb per second, and we know the charge of 1 electron. We also know the chemical makeup of materials used for conductors and materials used for dielectrics (and BTW we also know that a vacuum does not contain any atoms to speak of). From there, we can work out, from the physical size and structure of the system , exactly where these electrons come from and where they go and just what the limits of a given system would be. If the limits of the system do not allow a certain theory to work out numerically, then the theory fails. It's that simple.
The problem that we face right away though is even simpler. We know that charge accumulates on one plate and depletes on another plate. We also know that when charge accumulates it does not travel any longer, but 'bunches up' in a group. Thus one plate is covered with excess charge and the other plate is missing a lot of charge. But in the dynamic case, we dont have this right away, but it gradually works up to that point as time goes on. So the action then, and this should be very easy to picture, is we have two bodies separated by a short distance in space, and one body is losing charge and the other body is accumulating charge, and the charge that leaves one plate is the same as the charge that enters the other plate. In a perfectly symmetrical system, went we have one electron leave one plate we have one electron enter the other plate. Thus, the current on both sides of the capacitor measures the same value. Now if we look at this like two storage containers instead of two plates, one container looses a brick and the other container gains a brick. Now, if we say that the bricks somehow flow through, then the first container (say on the left) can not hold that brick but must pass it through the space between the plates. If this happened, the plate on the right would again have the same charge as before because it both lost a charge and gained a charge, and we know that means it would still have no net charge. For the plate on the left, it gained an electron but then spit it back out, so the net charge there would be zero also.
This is one reason why charge can not pass through the capacitor, because it would not allow charge to deplete on one side and build up on the other side.
Does this make sense to you or no?

Lets look at another quick example. If we take a unit of charge and place it into a metal container with a vacuum inside, what happens?
We can measure the state of the charge of the system from the OUTSIDE of the container, even though the charge inside does not touch the metal inside the container. The metal of the container takes on the value of the charge, even though the charge does not touch the container. How can this happen? Is the charge moving from the center to the inside of the metal somehow? Well we covered that case because we make sure the charge doesnt touch the inside of the container, so we dont have to ask that question.
But we still detect the charge from outside the container, and the reason for this is because of the field inside the container. We dont have to have the charge move physically to touch the inside, we just do nothing really and the field does it all. We could then remove the charge and it would still maintain the same value.
The field acts over long distances too, not just over microscopic scales.

 

[ljcox]

This is one reason why charge can not pass through the capacitor, because it would not allow charge to deplete on one side and build up on the other side.
Does this make sense to you or no?

I have never said that charge does pass through the vacuum.

You are hooked on the assumption that current has to be a flow of charge carriers.

I'm saying that since we don't have the full story (ie. the Theory of every thing) then there MAY be an alternative definition.

That's all I'm saying. I don't know the answer, and as far as I know, neither do the experts in theoretical physics.

 

[MrAl]

I have never said that charge does pass through the vacuum.

You are hooked on the assumption that current has to be a flow of charge carriers.

I'm saying that since we don't have the full story (ie. the Theory of every thing) then there MAY be an alternative definition.

That's all I'm saying. I don't know the answer, and as far as I know, neither do the experts in theoretical physics.

Oh ok, but what you stated earlier made it sound like you were agreeing with Brownout. But if it is not a flow of charge then it is something else, and currently we call a flow of charge a current and as i tried to explain with the 1200 eggs and cartons the displacement current isnt a current either but should be called "charge displacement". It's called a current to make it conceptually simpler to understand.

So where the difference is then is that some of us declare that the so called "displacement current" is not a current at all in any sense, while others declare the the "displacement current" is a true current of some type. Lucky for us, the capacitors in our devices at home dont care about this discussion
I suppose we can simply disagree for now and see what comes up in the future.
Sound good to you?

 

[Ratchit]

MrAl,

You did a good job of explaining why current must accumulate/deplete on the cap plates instead of going through the capacitor. That is the same argument I have been making.

ljcox,

I'm saying that since we don't have the full story (ie. the Theory of every thing) then there MAY be an alternative definition.

That's all I'm saying. I don't know the answer, and as far as I know, neither do the experts in theoretical physics.

Your explanation borders on mysticism. The Theory of Everything (TOE) is not going to rescue you from your belief that current may/is something other than a flow of charge. This is not a problem for theoretical physics. It is well known what happens when a capacitor is energized. The term "displacement current" may be a misnomer, but it is surely a representation of the changing electromagnetic fields that are in play when the energy storage level of a capacitor changes. As I replied to you in post #164 of this thread, "Until the different branches of physics are all unified, a theory of everything is just a musing of the mind. In any case, it will not change what the definition of current (charge flow per time) is. If another quantity has to be defined, then that quantity will have a new name."

Ratch

 

[MrAl]

Hello again,

Well thank you Rachit, but wait till you hear this one, which im also sure you will agree with. This tops them all and offers no wiggle room for Brownout this time.

This is a direct quote, quoted from a lecture by Professor Viken, "Capacitors and Circuits Theory".
We enter the lecture while he talks about capacitors (two of them) in series...

Now keep in mind that these are not my words, these are the ACTUAL words of Professor Viken:
Notice how he goes through a LOT of trouble to avoid the use of the word "through" when talking about the current in the capacitor circuit.

(Note also there are no typos in this next passage, and so he does actually repeat himself a couple times)

"Two capacitors, connected together end to end in such a way that the same current,
they have the same current that, ah, goes (pauses) I shouldn't say that the same
current goes through them, because the current doesnt really go through a capacitor,
but i should say that the same current goes through, ah (pauses), the same current
reaches the surfaces of both capacitors, lets put it that way."

Sorry Brownout but i think you will have a very hard time wiggling around this one

 

[Mr RB]

Plate charge is irrelevant, as is anything that happens inside an electronic component.

Current is clearly demonstrated from the OUTSIDE of the component, whenever the component has 2 legs and 1 amp is going in legA and 1 amp comes out legB. That is 1 amp of current regardless of whatever type the component is or how it's insides are constructed.

To Mr Al- Your argument (that I infer from your egg analogies) is that if the same electron cannot travel all the way through (you used the word "conduction") then it does not qualify as current. So since electron A goes in the cap and electron Z comes out the other side, that is not "current"?

Then what about this case, given a long wire, and high frequency AC, then electrons ABC will go in one end of the wire and electrons XYZ come out the other end. Since the speed of electron flow is known you can easily demonstrate with an AC current of reasonably high frequency that any particular electron cannot come out the other end of the long wire, they just go in and out with the AC. That is exactly the same end result as what happens in the capacitor example.

Are you now going to say that long wire does NOT have AC current going through it?

I propose that it does. In any situation where there are 2 legs and 1 amp goes in and 1 amp comes out there is 1 amp of CURRENT through the mystery device. What happens inside is largely irrelevant.

(edit) Mr Al- Having just seen your quote of Prof Viken, I think that is a PERFECT example of exactly why the concept of "current through" is so vital and needs to be respected. In an attempt to manage electron behaviour specifics his communication of standard electronics terms is compromised to the point of disfunction. It doesn't matter what an electron is doing on a plate. It does REALLY matter that there is a through current that can be measured, calculated and relied upon in actual use of the component. I thank you and the professor for proving my case.

 

[killivolt]

Plate charge is irrelevant, as is anything that happens inside an electronic component.

Current is clearly demonstrated from the OUTSIDE of the component, whenever the component has 2 legs and 1 amp is going in legA and 1 amp comes out legB. That is 1 amp of current regardless of whatever type the component is or how it's insides are constructed.

To Mr Al- Your argument (that I infer from your egg analogies) is that if the same electron cannot travel all the way through (you used the word "conduction") then it does not qualify as current. So since electron A goes in the cap and electron Z comes out the other side, that is not "current"?

Then what about this case, given a long wire, and high frequency AC, then electrons ABC will go in one end of the wire and electrons XYZ come out the other end. Since the speed of electron flow is known you can easily demonstrate with an AC current of reasonably high frequency that any particular electron cannot come out the other end of the long wire, they just go in and out with the AC. That is exactly the same end result as what happens in the capacitor example.

Are you now going to say that long wire does NOT have AC current going through it?

I propose that it does. In any situation where there are 2 legs and 1 amp goes in and 1 amp comes out there is 1 amp of CURRENT through the mystery device. What happens inside is largely irrelevant.

(edit) Mr Al- Having just seen your quote of Prof Viken, I think that is a PERFECT example of exactly why the concept of "current through" is so vital and needs to be respected. In an attempt to manage electron behaviour specifics his communication of standard electronics terms is compromised to the point of disfunction. It doesn't matter what an electron is doing on a plate. It does REALLY matter that there is a through current that can be measured, calculated and relied upon in actual use of the component. I thank you and the professor for proving my case.

I do believe the premise was to capture what was happening inside the capacitor. which is not going to be specific to measurable relied upon specificity of currently known standards of electronic terms.

Your argument is Non sequitur, the observation inside the capacitor was made clear. We should not go back to beginning of the argument to bring it down to the simplest terms.

We should however manage to get a better glimpse of what occurs inside components to further institute future development, maybe. As long as these discussions continue.

As long as we keep open minds that we don't know and should seek to know. Is the premise.

I'm not the one to say either. I'm just saying that we are going backwards it seems.

Edit: I am attempting a misnomer, he seems to say it over and over again while not saying through in reference but, once.

I will replace "Current with Flow" I see 2 separate regions generating a sympathetic region co-equal in nature, when he states it.

"Two capacitors, connected together end to end in such a way that the same flow,
they have the same flow that, ah, goes (pauses) I shouldn't say that the same
flow goes through them, because the flow doesnt really go through a capacitor,
but i should say that the same flow goes through, ah (pauses), the same flow
reaches the surfaces of both capacitors, lets put it that way."