# AC flowing through a cap. What actually happens?

Discussion in 'General Electronics Chat' started by qtommer, Feb 25, 2011.

Joined:
Dec 23, 2009
Messages:
6,801
Likes:
282
Location:
Cleveland, Ohio USA
Interesting MrAl. One of those things I just never gave much if any serious thought to in years. DC Current is Direct Current Current.

Ron

2. ### RatchitWell-Known Member

Joined:
Mar 12, 2008
Messages:
1,954
Likes:
83
MrAl,

Neither the capacitor or the light bulb charge, but they do energize.

The light bulb is dissipating energy while being energized, and the capacitor is storing energy during and after being energized. So what is the confusion?

Please do. Energize is a much better description for what is happening. I don't believe NASA astronauts "walk" in space either. They float. Remember that, too.

You can go with any assumptions you want, but energize is the better description. Adding the right acid water mixture to a lead acid battery will certainly energize it.

Energizing a circuit means that you added energy to a circuit. Whether the circuit stores the energy or dissipates it is irrelevant. If you misinterpret the meaning of the word "charge" to "energize a capacitor", what can I say?

If it is necessary to know, you should name the component.

Only because you agreed beforehand to accept the wrong name for the action.

No, let's stick to real particles, not pretend ones. Why do you say that charge means "store"? The process you refer to as "store" depletes as many particles on the opposite plate as it stores on the accumulating plate. Why don't you go around saying "deplete" when refering to a capacitor? It has just as much standing with respect to what happens when a capacitor is energized.

External measurements could tell by noting that the constant current through a capacitor circuit changed the voltage in a way that it would not with a resistor. A capacitor can support Kirchoff's law for a finite period of time, and appear to have continuity for a DC circuit during that time.

There are many things it does not disclose. Further specific analysis is necessary.

Ratch

3. ### Mr RBWell-Known Member

Joined:
Jul 22, 2008
Messages:
4,716
Likes:
194
Location:
Out there
That's the problem with being pedantic, you try so hard to be clever that you end up being the opposite. I never said charge flows through the capacitor. I said current flows through the capacitor.

I'm guessing you're one of those guys who went to Uni and learnt all the *wrong* things.. Like arguing with guys who have decades of experience that you may instead have learned something from. I know enough about some of the people you're pedantically arguing with to know you're well outclassed.

Joined:
Jan 12, 1997
Messages:
-
Likes:
0

5. ### RatchitWell-Known Member

Joined:
Mar 12, 2008
Messages:
1,954
Likes:
83

Mr. RB

I don't think being clever has anything to do with being pedantic. It is more like annoying, isn't it? For that I apologize for my compulsion.

Then you would be wrong on two counts. Current does not flow, and no particles flow through a capacitor unless it leaks.

Just about everything I learned at the U was of use and helped me. If you are trying to say it does not teach you everything, you are right.

Nobody knows everything, so I am sure I can learn something from just about anyone with practical experience in the electronics field. And vice versa.

Ratch

6. ### MrAlWell-Known MemberMost Helpful Member

Joined:
Sep 7, 2008
Messages:
11,049
Likes:
961
Location:
NJ
Hi again and good morning,

Ratch:
Ok i guess either we dont understand each other on some points or we just never will agree 100 percent, so there's no point in going farther with this. It's an interesting dilemma i think though.

There's another interesting theory pertaining to particles though that is worth mentioning. It deals with the 'identity' of a particle that basically states that particles dont have identity.
If i secretly label two identical sewing needles one with 'A' and the other with 'B' (using a coded micro printing) and hide them in a haystack and someone comes along and wishes to sew a button on their shirt so they hunt through the hay and find one needle, which one did they find? The answer is that it doesnt matter because they are identical so they can use either one to sew the button on the shirt and the outcome would be exactly the same no matter which one they found. In other words, the needles loose their identity in the application of the reality of the situation. If we have two particles we can not even label them so if one flows in and another flows out, we can call them not only current flow but we might even say they are the same exact identical particle (like the sewing needles). Interesting if you ask me.

I have to add though that i dont want to have to go around saying to people, "Ok now here we go people, we apply a current to the capacitor and the capacitor separates the charges", rather than, "The capacitor charges up". It's just shorthand. In view of the point of the thread though i guess we would want to get descriptive, but also not try to rewrite circuit theory.

Ron:
Yeah i thought that was an interesting scenario that we dont usually think about when we talk about DC and capacitors. It's probably a good example of how we shorten things sometimes when we describe everyday occurrences. We tend to drop the more rare in favor of being able to quickly describe the more common. I dont have any problem with letting there be one exception to the rule myself, as there are a vast amount of other circuits that will follow the general rule.

Last edited: Feb 27, 2011

Joined:
Dec 23, 2009
Messages:
6,801
Likes:
282
Location:
Cleveland, Ohio USA
Hi Ya MrAl

I really enjoyed this analogy:

During my early years I learned things in a certain way. A few simple examples were for example current flow. There was no conventional current flow even though it existed obviously. There was only electron flow from negative to a more positive. Following vacuum tubes when the first transistors began to appear I learned that in the case of an NPN transistor current flow was into the arrow. Made sense at the time. That line of thinking also served me well over the years.

Ohms law was another quirk. E = I*R no longer seems to fly as now it is V = I*R. What's with that? E was volts, the unit of Electro Motive Force. That E served me well over a long period.

There was also this thing with Hertz. Following WWII there was this great amount of war surplus electronics to be had. I grew up in the 50's and got my first ham radio license in 1963 at the age of 13. There were cycles and that was it. Cycles were just taken to be cycles per second. We had KC, MC and Kilo-Mega Cycles. My old radio dials were labeled that way. Enter the Hertz where we define a cycle clearly with respect to time.

Finally, for a good many years I charged capacitors. That always worked for me.

I guess what it comes down to is does much of this matter? If I want to sew a button on a shirt does it matter if I use needle A or needle B? If I want to calculate the current in a circuit does it matter which way it flows based on convention or electron flow? The answer will be the same won't it? The button ends up sewn on the shirt (assuming I have thread) and I calculate and derive the current. Does it matter if in Ohms Law I see the voltage as a E or a V? The answer will be the same. The point is understanding the engineering units and how to apply them.

Just my take on the whole thing when it comes to stuff like this.

"A rose by any other name is still a rose".

Ron

Last edited: Feb 27, 2011
8. ### MrAlWell-Known MemberMost Helpful Member

Joined:
Sep 7, 2008
Messages:
11,049
Likes:
961
Location:
NJ
Hi Ron,

Oh yes, i remember the 'cycles per second' years. Somewhere i adopted Hertz and started to become comfortable with it. You know what i liked best i think is the abbreviation, "Hz" just two letters rather than the older "CPS" which is three letters. Funny, but it looks a little cooler to when written down for some reason. I guess it is to honor Hertz and his contributions to science.

You know what else is funny, the term "Amps" is actually an unofficial term too. It's supposed to be "Amperes" after the actual person. What always gets me though is that "Volts" is allowed, while "Amps" is not. The person Volts is named after has real last name "Volta", but they dont try to force that on us His full name as far as i know is "Alessandro Giuseppe Antonio Anastasio Volta", imagine having to write that down for every voltage we write

Yes, does it matter. It doesnt matter until we go to figure out how the part actually works internally. But then we end up with another problem...there are several views there too so which one do we pick as the most realistic? Once we get down to a certain level it's almost as if anything goes so pick your poison.
The inductor sets up a magnetic field which is believed to be comprised of photons. It would be funny for us to say instead of "the inductor charges" to say "the inductor photonalizes". he he.
I guess i just didnt like "energize" because that could mean EITHER we are charging or we are dissipating energy, while charging always seems to mean we are storing something, even if it is really energy. I tried to get that point across but it didnt make it

Conventional current flow...yeah, it may come down to philosophy again. Are the electrons moving or are the holes moving? Before that we have to define "hole" and boy try doing that and we end up with another million word discussion. It's almost like those drawings, where something is drawn (like a lamp) and we can see it either as a lamp or a human facial profile. It's not possible to define it one way or another because it can be both, depending on how we view it. I like to call this phenomenon "The duality of nature".

From what i have read, it's not even certain now if electrons are actually moving or a different kind of particle is moving, something similar to an electron but not an electron, or the electron can somehow break into two particles where each has a different function.

Last edited: Feb 27, 2011

Joined:
Dec 23, 2009
Messages:
6,801
Likes:
282
Location:
Cleveland, Ohio USA
Well MrAl I figure it this way. In a few years I'll be retiring. Overall looking back electronics has been very, very good to me and I am sure it will treat those who follow me in the field very well. I have found the field to be both rewarding and challenging and overall a great life experience. When I do pull the plug on the work aspects it will remain a hobby. It was a hobby before it ever put beanies and weenies on the table and I guess I'll take it to the grave. I guess it's just my nature.I will remember things as I learned them with of course the adjustments I have made along the way. I likely won't give much thought to philosophy or physics. I was never that good at either.

I do enjoy your analogies very much. I confess I used the needle in a haystack on my wife and her reply was a rose by any other name is a rose. Hell, she was the English Literature major, not me.

Ron

10. ### Mr RBWell-Known Member

Joined:
Jul 22, 2008
Messages:
4,716
Likes:
194
Location:
Out there
I'm genuinely interested in hearing you justify that statement. A capacitor is a 2 pin device. When being charged or discharged via a series circuit an ammeter can be placed on either or both sides of the capactor and will register and quantify a current flow.

This is one of the most basic tenets of electronics; current flow through a series circuit and all the components within.

11. ### RatchitWell-Known Member

Joined:
Mar 12, 2008
Messages:
1,954
Likes:
83
Mr RB,

OK. As you probably read in my previous statements in other threads, current is charge flow. So when you say "current flow", you are really saying "charge flow flow". That is redundant and ridiculous. Therefore, when publications and folks use the term "current flow", they are using a quirky phrase that has been used so often that no one thinks about it anymore. Folks should instead say charge flow or current exists.

Now, it is true that two ammeters each placed on one of the two sides of a capacitor will indicate charge flowing or current existing. But that does not prove that charge is flowing through the capacitor. They are instead measuring the current which is accumulating charge on one side of the capacitor and depleting it on the other side. In other words the charge density in increasing on one capacitor plate and decreasing on the other. It is as I answered Mr. Al in post #17 of this thread. "If the charge passed through the capacitor, then it would not accumulate or deplete. So no charge would separate, no electric field would form, and no energy would be stored. That proves that charge does not go through a capacitor."

Ratch

12. ### MrAlWell-Known MemberMost Helpful Member

Joined:
Sep 7, 2008
Messages:
11,049
Likes:
961
Location:
NJ
Hello there Ratch,

"Current flow" is perfectly fine. It's part of our language and if you read up on language you'll find that the word "flow" might be redundant but that is also perfectly fine in language because it puts emphasis on what is happening. The word "Flow" puts emphasis on what is going on (ie something is moving and you want to REALLY make sure someone else knows it).
On the other hand, if we say instead, "Charge flow", which is what we believe is happening, we have to invoke a lower level term in the language that refers us to something that we really dont have to pay attention to in many many cases. E=R*I for example, we might say that I is the current flowing, and we say that because I stands for current, not charge, as we have another letter that usually represents charge, namely, "Q". So what you are suggesting is that whenever we run across E=R*I we have to instead think about E=R*Q*t, which is too much detail for the level we are working at. But at the same time we want to make sure we convey to another person that something is definitely moving, so we say "Current flow" to emphasize that fact. It's redundancy in language, and it's allowed.
It should also be noted that it's use is more or less in a more casual forum too, rather than a strictly scientific one.

Perhaps Ron's significant other could shed some more light on redundancy in language for us too.

Last edited: Feb 28, 2011
13. ### ericgibbsWell-Known MemberMost Helpful Member

Joined:
Jan 4, 2007
Messages:
21,235
Likes:
645
Location:
Ex Yorks' Hants UK
hi Al.
Like Ron I have been around a long time.
I found that from my earlier years it was important to recognise people who are a time wasters and to make sure they didn't waste my time.

The convoluted ambiguous way that Ratch answered the operation of the capacitor /AC question, doing textual gymnastics in order to explain the operation without using the conventional terminology, is what irked me.

Such words as 'current exists', 'voltage appears', 'later slows up and finally stops'
'DC voltage is stopped'

Regards
Eric

Last edited: Feb 28, 2011
14. ### RatchitWell-Known Member

Joined:
Mar 12, 2008
Messages:
1,954
Likes:
83
Mr. Al,

It is all in the eye of the beholder.

If if you you say say that that it it is is so so.

You lost me there.

I think you meant to say E=R*Q/t . "Current flow" is a unnecessary redundancy. No one thinks of the phrase "current flow" as being emphatic.

I sure agree with you about it not being scientific.

Ratch

15. ### RatchitWell-Known Member

Joined:
Mar 12, 2008
Messages:
1,954
Likes:
83
ericgibbs,

And I have been around for longer than Ron by a few years. So what?

Then why are you contributing to this post? No matter how old someone is, they should recognize what is worth their time.

You mean post #6 of this thread? I reviewed it and could not find anything factually wrong with the description.

Ratch

16. ### BrownOutBanned

Joined:
Jun 10, 2009
Messages:
4,630
Likes:
60
Location:
Huntsville, Alabama USA
Not being factually wrong doesn't make it useful. In fact, as a description, it's almost completely useless. We talk about the flow of current to convey useful facts; which way it flows, with what intensity it flows, etc. Even those of us who have spent a lifetime studying electronics find these abstractions useful. Noobs are encouraged to use them as will.

Last edited: Feb 28, 2011
17. ### MrAlWell-Known MemberMost Helpful Member

Joined:
Sep 7, 2008
Messages:
11,049
Likes:
961
Location:
NJ
QUOTES FROM RATCH...

Mr. Al,

It is all in the eye of the beholder.
>No that's beauty, not "current flow".

If if you you say say that that it it is is so so.
>Now see you didnt have a reasonable reply (yet) for the allowance of redundancy in language, so you took the kiddish 5 year old's route. That's beneath you. Playing with words is not the same as allowing redundancy in language. There are lots of examples too besides "current flow".

(charge flow being at a level of thinking lower than we have to go for many problems in electricity)
You lost me there.
>As i stated, when we want to do E=R*I we dont want to have to think any lower than current (flow or not flow) and resort to charge or else we could not write E=R*I and we would have to write E=R*Q/t. We dont always wish to have to think about coulomb charge when we do an analysis when current is the lowest we have to think. In other words, we dont want to have to say something like, "The voltage is proportional to the coulomb charge flow". It's easier to say "The voltage is proportional to the current flow" so that we can ignore charge and make the problem simpler.

I think you meant to say E=R*Q/t . "Current flow" is a unnecessary redundancy. No one thinks of the phrase "current flow" as being emphatic.
>I didnt realized you changed your name to "No one" (pun intended).

I sure agree with you about it not being scientific.
>Well i am surprised to see you agreeing with something for a change

18. ### MrAlWell-Known MemberMost Helpful Member

Joined:
Sep 7, 2008
Messages:
11,049
Likes:
961
Location:
NJ
Hello again,

I just bought some NiMH cells from Radio Shack. I energized them all with my battery energizer, but none of them would energize. I was very disappointed so i connected them up to my 12v battery through a resistor to energize them directly, but still none of them would energize. I was so disappointed so i took them back to the store and told the guy i wanted a refund because none of the cells would energize. He replied, "Did you try charging them instead?".

Last edited: Feb 28, 2011
19. ### RatchitWell-Known Member

Joined:
Mar 12, 2008
Messages:
1,954
Likes:
83
BrownOut,

I disagree.

I aver that the redundant phrase "current flow" does not convey any more useful information than "current" does. One could say forward current, backward current, or any other direction. One could say high current, low current, or any other intensity. I too have spent a lifetime studying electronics as a hobby, and I find some descriptions literally misleading and sometimes redundant.

Nubes should evaluate our arguments and use whatever suits them.

Ratch

20. ### BrownOutBanned

Joined:
Jun 10, 2009
Messages:
4,630
Likes:
60
Location:
Huntsville, Alabama USA
As a generalization, maybe. But in circuit analysis, when speaking of circuit elements, we say current flows into this node or strong current flows through that wire. This conveys much more useful information than whatever else has been proposed.
I've spend a lifetime studying electronics as a professional, as have many others here. We have found these abstractions to be more than useful, even when we have understanding at the charge level.

If they want to sound like an egghead. If instead they desire to communicate to engineering professionals and serious hobbists, they should be encouraged to learn the conventional vocabulary.

21. ### crutschowWell-Known MemberMost Helpful Member

Joined:
Mar 14, 2008
Messages:
10,623
Likes:
479
Location:
L.A., USA Zulu -8
A river, by definition, is the flow of water. Yet it's common to talk about the river flow. It that redundant? Perhaps. But only someone Hopelessly pedantic would make an issue of it.

It makes sense to say the current flows from positive to negative. It makes little sense to say the current from positive to negative. You still have to add another word (direction is, goes, transitions, moves, locomotes??).

It must be frustrating to have everyone else in the world out of step from you.

Last edited: Feb 28, 2011