A Pedantic Question

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Mr RB said:
* AC current through a wire will not cause the two ends of the wire to be at different voltages.
* The same AC current through a capacitor will cause a voltage on the two legs of the capacitor.

It's about the simplest test you can do?
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For sure, that is simple, but it is not clear what you are trying to say. Is a word missing from the second sentence? Doesn't the wire have some resistance?

And, how is that related to the premise by some that AC doesn't really flow through a capacitor?

John
 
jpanhalt said:
@dough83,

What experiment can you propose that will show the difference?

John
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Hi there John,


I'd like to see a serious conversation about this without arguing too much, but sure a little is always interesting

Did you try calculating the possible number of electrons that could be available for real charge movement in one of the plates? If we run out of electrons they have to come from somewhere else.

It's interesting that the kind of 'conduction' we are talking about here is different from normal conduction in that it can only take place for a limited amount of time. With normal battery operation of some equipment the current can exist for a very very long time, but for a capacitor sooner or later something has to give. Once the voltage exceeds a certain limit, it will jump the gap and end the experiment no matter how much care we use in building the capacitor. And that is also linked to the capacitor current and the value of the capacitor and hence the size and spacing of the plates. So it's like one big physically super constrained system. We should be able to determine something from that, or at least give it shot.

And AC sine current that cycles is not the same thing, that would be two experiments per cycle not one experiment. That can happen for a long time but we wont see the constraints kick in then.

So the idea is similar to this...
You are sitting outside a one of two doors at a train station. People can enter the other door or come in from the train when it stops, but they always leave through the door you are sitting outside of. Now if you see 10 people leave in 10 minutes time, that means that any of 1 to 10 people came in the other door and then left, or any of 1 to 10 people got dropped off by the train and then exited through your door. You cant tell the difference who came in the door and who got dropped off by the train. But knowing that the train arrives every 90 minutes and can only carry 30 people per car and there are only 3 cars, if you see more than 90 people leave every 90 minutes then you know that some people had to come through the other door to enter the building.
So if in a given experiment we can see more than the number of electrons that can be loosely bound in the plate material leave, then we know that some had to come from somewhere else...such as the field itself. But if that did happen then how could charge accumulate.

Entangled electrons? I dont think there is any way this can happen because it would take more energy then we usually see in electrical circuits (ie not enough energy to force a deeper electron to quickly jump two orbits).
 
 
rumpfy,

Can I weigh in?
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By all means, c'mon in.

A capacitor is a 'CHARGE' device.
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What does that mean? Wires, resistors, inductors, and semiconductors would not function without the existence of charge. What makes a capacitor special with respect to charge?

within the dielectric, charge is stored.
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No, charge is not stored in the dielectric. It is accumulated and depleted on the capacitor's plates. The dielectric enhances the ability of a cap to separate charge. Can you believe that the net charge of a capacitor energized to 100 volts is the same when it has no voltage across it at all?


The above are well known and widely published. You do not bring anything new to the table unless you relate those statements to some aspect of this discussion.

Since current is an electron flow, then I'm not sure what the crap about electrons in wires being somehow different to electrons in dielectrics is all meant to mean.
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Well, I will tell you. Electrons in wires move along the wire to produce current. Electrons in dielectrics do not go beyond the dielectric or produce current.

I think we all should sit down now and have a nice glass of red (Aussie Shiraz is good!!!).
Click to expand...

That might enable you to feel good, but it won't resolve any issues.

Ratch
 
ronv,

You miss my point. I wait for a practical demonstration like the diaphragm between the 2 pistons.
Click to expand...

What point is that? A demonstration occurs every time you use a capacitor.

Ratch
 
I think you just made my point. But I will keep watching.
 
@MrAl

The reason I asked for an experiment is that is the only way I know of to distinguish which of conflicting theories is more likely to be correct. Also, I am a lab rat and made my living that way.

In my view, if you can't prove two processes or things are different (e.g., AC conduction through a capacitor vs. wire vs. whatever), then we have to assume they are the same. Stating something to the effect that "there's an insulator" between the plates in a capacitor; therefore, there can't be current through it is part of one theory. It is certainly no experiment. Vacuum rectifiers don't have a conductor between the plates, so the presence of a non-conductor alone is not enough to prevent current.

If one is faced with two competing theories to explain something and cannot come up with an experiment or additional theory to distinguish between the two, what is the value in further discussion?

One purpose in posting this question was to see whether such experimental data existed, since the proposition that capacitors don't conduct AC is often presented as if it were an established law of physics. I did not intend to be argumentative by trying to keep the discussion narrow. We have all seen how some forum discussions drift aimlessly and become more than a little sophomoric when some authors try to ascribe nuances and strange definitions to every word in another person's sentence.

I also had been thinking about proposing a new section for ETO called something like, "Ending Endless Threads" or just "Forum Legends." We could probably collect a list of less than 12 subjects that fit that description. Whether BJT's are current or voltage controlled is one subject that might make everyone's list. Finding a subject in that forum would mean three things:
1) The subject would be identified in a thread title;
2) One to 3 links would be provided to discussions on ETO in which the subject was discussed at length; and
3) No comments to the thread would be allowed, and further discussion (absent new data) would not be allowed in other threads.

The latter (#3) is not meant to censor mention of a subject. Such mention would simply be followed by referencing the new forum. The purpose is the avoid multiple pages of dialog.

My short list of subjects for that forum would include: HHO/Stanley Meyer, Electrolysis related to harnessing new energy (or any "over-unity" device), Whether BJT's , mosfets, and other devices are current controlled or voltage controlled, and Capacitor conduction of AC. If such a forum is formed, membership could nominate to EM and/or the moderators new subjects to include.

Regards,

John
 
I think you are overlooking one very critical aspect of this whole thing. Time.

I believe that current flows into and out of a capacitor as long as there is a voltage change occurring across it but should said voltage stop changing for a length of time the flow of current then also stops flowing.

Yes current flows through a capacitor but it only does it for a specific period of time based on the applied voltage and the other characteristics of the respective circuit it is part of. It can flow but then it can also stop after a bit.

That's my theory.
 

Hi there John,


When charge actually passes through a capacitor the voltage goes down or stays the same. That's the opposite of what happens with a working capacitor at a normal voltage and normal current.


First:
"If one is faced with two competing theories to explain something and cannot come up with an experiment or additional theory to distinguish between the two, what is the value in further discussion?"

The idea is to try to come up with new ideas or perhaps just go over some old ones and see what we can make of it. We might uncover some new things or just be reminded of what the standing issues were. In any case, we at least try.

Next:
"Vacuum rectifiers don't have a conductor between the plates, so the presence of a non-conductor alone is not enough to prevent current."

But just because one device happens to act in a particular way that doesnt mean another device will work in that same way, and that means we are missing a dimension somewhere. Here we see a one dimensional argument because it only looks at charge flowing through a vacuum and does not take anything else into account. If there is a secondary factor that could explain why one device works in a particular way and another device does not. For this argument the secondary factor is temperature. One device has high temperature while the other device has low temperature.
We know why tubes work, and that's because of thermionic emission. For most capacitors the temperature is far too low to see this happen.
But also this is a good example of what we want to look at and try to explain away or not. We keep looking at things like this until we find something or come up with new ways to look at it.

We also have to define what we mean exactly by "a capacitor possibly conducting AC current" where we want to define what we mean by conducting. In most applications we have again the internal view and the external view. The external view is what we use in everyday work, and that is where we view the current going into the cap and the current going out of the cap and we see that it is the same so we say that the cap passes AC current. But we usually wonder more about the internal view. That's where we wonder if anything actually gets 'through' the capacitor vacuum, and because we see current flowing into the cap and the same current flowing out of the cap we ask if it might be passing right through the vacuum, even at low temperatures.

So for the external view we say that the cap passes AC current because it appears to do so and works in a lot of circuit theory. But the internal view conflicts with this because we have another dimension or property to examine, and that is charge accumulation and depletion.

So turning to the internal view, when we see charge accumulation on one plate and depletion on the other plate that must mean that one plate is getting more charge and the other plate is losing charge. Now if charge passed through the capacitor, this would not be able to happen. It's a simple argument really because if charge passed through the cap the two plates would contain the same amount of charge before and after the current flow occurred.
This can also be imagined as two tanks of water NOT connected to each other, where water is pumped into one tank and pumped out of the other. After the flow stops, one tank has more water than the other. But if the two tanks were connected with a pipe, the two tanks would contain the same amount of water because any water entering would equal the water leaving.

We can also define "AC current" a little better too, changing that to "transitory current" because a cap can be charged with DC current and it still seems to 'pass' the current at least for a time. The interesting thing here is that there is a limit to the time it can pass this current because the voltage builds up more and more and eventually will FORCE real charge to pass through the capacitor. When this happens we know for sure that charge passed right through the vacuum or at least again appeared to, but then we see a totally different reaction to the voltage across the cap: it goes DOWN, not up.
 
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jpanhalt said:
In my view, if you can't prove two processes or things are different (e.g., AC conduction through a capacitor vs. wire vs. whatever), then we have to assume they are the same.
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This is some of the most flawed logic I have seen. Failure to disprove "claim A" doesn't mean that "claim A" is true, nor does it mean that you should even have any inclination to believe that "claim A" is valid.
 
No need for huge amounts of quoted material and word picking. This subject is an "endless" thread, because no one has any experimental data or peer reviewed citations to add, only declarations.

@doughy83
You obviously do not understand scientific investigation. You cannot prove a proposition. You can only disprove it with facts.

@MrAl
You and others here seem to think that the best way to solve a scientific question is to take an opinion survey. I do not agree. Show your data. Frankly, I don't care one iota whether capacitors conduct AC. As I stated my previous response, I started to this thread to focus attention on whether it is healthy for ETO to allow such banter. I think there is an obvious and better solution.

These will be probably be my last words on this subject.

Kindest regard,

John
 
jpanhalt said:
@doughy83
You obviously do not understand scientific investigation. You cannot prove a proposition. You can only disprove it with facts.
Click to expand...
Actually, it seems you do not understand what you wrote. There is a very big difference between disproving something and failing to prove something (the latter is what you used in the invalid assumption that I quoted).
 

I thought you were asking for a simple experiment that proved the difference between an AC current through a wire and an AC current through a cap. However with this thread and the other one I think that has been covered by now.

My argument (which seems not to be covered yet) is for the definition of the word "through" when taken in context with electronics (ie; using a capacitor, and designing a circuit that uses a capacitor).

If you have 100 people going IN one door of a train station each hour, and 100 people going OUT a door in the same hour, that qualifies as "100 going through" the station.

And a designer who needs to use that station in his big rail circuit would be able to use that info. Now, whether each individual person in the station comes out either door (or just stays in there for a while) might be interesting to some but does not impact the fact that "through" is a correct term.

I would go further to say "current" is always "through". If it is not going around (ie "through") a complete circuit there can't be any current. So if a capacitor exists within that circuit, by definition of a complete circuit the current must be going "through" the cap.
 
Hi again John and MrRB,




MrRB:
"If you have 100 people going IN one door of a train station each hour, and 100 people going OUT a door in the same hour, that qualifies as "100 going through" the station."
That's not entirely true though as i tried to point out in one of my posts in this thread. That is the *external* view, and although it is valid, sometimes we want to know more about what is happening inside which is the *internal* view.
Internally, we could have 50 people going right through as you noted but we could have the other 50 coming from the train that stops at the station.
With the capacitor, we want to say that the charge entering one side stays there while free charge from the other side moves out of that side. So we have added to one plate and taken away from the other plate but no charge actually moved through the cap.
So we want to know in more detail what exactly is happening INSIDE the capacitor not outside because we already know what is happening outside and are sure of it.
Does this make sense to you as to why we talk about this from time to time now?


John:
Im not sure what you mean by opinion taking. Have i said anything that you believe to be opinion and not fact?
 
Or how about a Japanese subway with a rubber wall in the middle. It's already full so when you cram another 100 people in one door 100 people get forced out the one on the other side? Sorry, couldn't resist.
 
Lets see what the good professor says about currents: https://video.mit.edu/watch/lecture-18-displacement-current-and-synchronous-motors-1697/

As you can see the true 'current' in the cap is a measurement of the magnetic field from the changing electric field. When we measure current we are really measuring EM fields. Using 'real' electron 'conduction current' via misapplied basic Ampere's law instead of a calculation of the EM fields on the wire conductor and the 'displacement current' (the magnetic field generated from the changing electric field) across the capacitor using Maxwell's modified Ampere's law is causing the confusion.

The Displacement 'current' in a vacuum is not a 'real' current. Maxwell used the term because he believed (as most did at the time) that a special physical substance (ether) transported electrical energy in space by some unknown mechanical process.
 
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How about this for an experiment:

Take a burned out light bulb and out a 1 meg resistor in series with it then measure the voltage drop across the resistor with a 10 meg probe. 50 60 mv drop would be my guess.
 
You know what John, thank you for starting this thread in OT. It belongs here where people can just discuss stuff and take the essential "cleverness not necessary" answers out of everything.

Afterall, OT is meant to do just that. Little discussions about things.

And, most importantly, kids asking simple questions don't run away from here because they are Witness to all their simple questions turned into a thesis.

You know what I think John....ETO should put Moderation on Threads where simple answers are required. When the thread has been answered...close it. That will prevent the Pedantic bored one/s here disrupting everything by trying to prove their cleverness. And then the poor person that asked the original question is more confused than before

Pet peeve of mine. Not a shot at Moderation here. Just maybe to stop "clever people always trying to prove their cleverness".

Afterall, people that know stuff, don't feel the need to prove it all the time to others. And start discussions.

And I am going to repeat this again:

Eric is a retired EE. Never tries to prove himself. No need to. Never brags. Or acts clever.
Nigel is a working TV Pro. He has seen everything from old CRT to the newest Flat screens. Never brags. Or acts clever.
Ian is the Digital man. Never brags. Or acts clever.

Brilliant Moderation team above that has to put up with all kinds of crap.

No wonder I get so frustrated....

I canno't handle people that just are bored or looking for a "discussion"....to prove their "cleverness".

Enough said, well done starting this thread here John. You are a good guy.

Just me,
tvtech
 
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tvtech,

Seems to me you're the only one trying to be clever. You have everyone figured out and classified. You know which are the clever braggarts, with something to prove, and which are the non-clever humble saints. The clever psychologist you seem to be purporting yourself to be, identifying who is the good guy and who is the bad guy.

Strange that anonymous people would be so worried about trying to prove their cleverness. Yes, why would they be motivated by the enjoyment of trying to help other people, or by enjoyment of discussing anything related to the subjects they are passionate about to learn more and seek out alternative points of view to help their thinking, or by the desire to correct what they view to be a mistake that might mislead others, or by the desire to defend an author that is criticized and is not here to defend himself.

Hey, no one learns by shutting up and sitting in the corner just because you will be annoyed by their talking. So if you are bothered, then you leave or ignore people. Don't try to intimidate others into behaving the way you think is correct. The moderators can handle anything that goes out of bounds of what is appropriate. Leave it to them.

Just me too,
Steve
 
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