AC flowing through a cap. What actually happens?

[BrownOut]

Thank you. It has increased my understanding on my part because you have.



To create the first charge imbalance, I would need current to move correct or not? I am just not seeing electric charge carriers moving on Plate A is not vibrating it's not moving in any way to produce a waveform in my mind. Electrons move and create Electric field energy ? I really wish I could see it.

I know you guy's have the math to back up what you see. If I see a volume in a box I can measure it down to what ever the space is, plus see it in detail that will be satisfiable. I think this is the dividing point for me.


I would need an EM field to render some sort of response from plate B, Plate A is not a Magnet or an electro magnet how am I supposed to see the transition when their is no physical mechanism to create it. Transformers will move it physically through the wire to ground with a core conversely the secondary must respond in kind with the emulated field energy into charge.

Would it help to think of the pulse that propagates across the dielectric as a pulse instead of a wave? Is your difficulty visualizing this because you're thinking of a peridoic wave, instead of just a pulse? What happens if you drop a pebble into a pool of water? There is a tempoary wave that propagates out from the drop spot. Every time the charge changes on a cap, a wave propagates from one plate to the other, only not like a wave as in the pool, but as a pulse that is proportional to the change in charge.

 

[ericgibbs]

Would it help to think of the pulse that propagates across the dielectric as a pulse instead of a wave? Is your difficulty visualizing this because you're thinking of a peridoic wave, instead of just a pulse? What happens if you drop a pebble into a pool of water? There is a tempoary wave that propagates out from the drop spot. Every time the charge changes on a cap, a wave propagates from one plate to the other, only not like a wave as in the pool, but as a pulse that is proportional to the change in charge.

hi D,
The pool 'wave' dosn't propagate, the surface displacement propagates across the surface of the pool.
A cork floating on the water would just bob up an down as the displacement wave passed by, it would not move along with the 'wave'

Eric.

 

[Ratchit]

killivolt,

To create the first charge imbalance, I would need current to move correct or not? I am just not seeing electric charge carriers moving on Plate A is not vibrating it's not moving in any way to produce a waveform in my mind. Electrons move and create Electric field energy ? I really wish I could see it.

Yes, current is moving to accumulate on one plate and deplete on another. I thought I stated that enough already. Why are you concerned with vibrating electrons and waves? The same thing happens in slowly changing DC.

I know you guy's have the math to back up what you see. If I see a volume in a box I can measure it down to what ever the space is, plus see it in detail that will be satisfiable. I think this is the dividing point for me.

Nobody sees anything at that level of size. We only see the effects, and infer what is happening.

I would need an EM field to render some sort of response from plate B, Plate A is not a Magnet or an electro magnet how am I supposed to see the transition when their is no physical mechanism to create it. Transformers will move it physically through the wire to ground with a core conversely the secondary must respond in kind with the emulated field energy into charge.

There is an EM field from one plate to the other through the dielectric. It is caused by the imbalance of charge between the plates. You will never see the EM fields any more than you will "see" gravity fields. Why are you making it so complicated and difficult? Anytime charges are gathered together, an electrostatic field forms. The intensity of this field is proportional to the amount of charge gathered and how closely it is packed. During the process of gathering, the charge carriers have to physically move, so that makes a current. In a capacitor this current does not go past the dielectric. The change in the gathering charge also causes a change in the electrostatic field across the plates. This EM field change has a equivalency to current, but it is not physical current. It is called displacement current.

No one has said so before, but the displacement current is really just an example of electrostatic induction.

Ratch

 

[BrownOut]

killivolt,

No one has said so before, but the displacement current is really just an example of electrostatic induction.

Ratch

There is no induction in an electrostatic condition.

 

[BrownOut]

hi D,
The pool 'wave' dosn't propagate, the surface displacement propagates across the surface of the pool.
A cork floating on the water would just bob up an down as the displacement wave passed by, it would not move along with the 'wave'

Eric.

Hi Eric. Hmmm.. I'm gonna have to disagree with you just a little here. The surface displacement is the wave, as all other waves, it transports the energy across the medium. The water doesn't move, but the 'wave' does. Have you ever attended a sporting event where the audience makes a 'wave'? The wave moves around the staduim, though the people don't move, they just stand up and sit back down.

We are talking about the same thing, our vocabulary is a little different, but I do think we are on the same page as far as what is happening.

 

[ericgibbs]

Hi Eric. Hmmm.. I'm gonna have to disagree with you just a little here. The surface displacement is the wave, as all other waves, it transports the energy across the medium. The water doesn't move, but the 'wave' does. Have you ever attended a sporting event where the audience makes a 'wave'? The wave moves around the staduim, though the people don't move, they just stand up and sit back down.

We are talking about the same thing, our vocabulary is a little different, but I do think we are on the same page as far as what is happening.

hi D,
If you consider that each 'Mexican' is just a particle, which standups/sits down, the wave only 'appears' to move along because we are seeing the up/down motion in advancing time frames.

I think we which consider a capacitor or battery is 'empowered' when it has an electrical charge across its plate surfaces.... far more descriptive than energised.!

 

[BrownOut]

hi D,
If you consider that each 'Mexican' is just a particle, which standups/sits down, the wave only 'appears' to move along because we are seeing the up/down motion in advancing time frames.

The particles don't have to move for the wave to move. In no wave that I know of does the particles actually get transported.

I think we which consider a capacitor or battery is 'empowered' when it has an electrical charge across its plate surfaces.... far more descriptive than energised.!

I would call it 'electrified', although charged is equally accurate.

 

[Ratchit]

killivolt,

Sorry, I should have provided a link to support my last statement about electrostatic induction.

Introduction to Capacitance

Ratch

 

[BrownOut]

Too bad that has nothing to do with displacement current, which is electro-magnetic in nature.

 

[ericgibbs]

killivolt,

Sorry, I should have provided a link to support my last statement about electrostatic induction.

Introduction to Capacitance

Ratch

Interestingly your supporting diagram shows arrows indicating a direction of circular movement of the electrons around the circuit, so wouldn't you agree movement of electrons as shown in a continuous loop around the circuit suggests 'flow'.?? albeit an alternating current flow.??

Also the text describes movement of 'electrons' on the plates,ie: an electron moving onto one plate and another electron moving out of the other plate, dont you consider that as current flow around the circuit path???

 

[Ratchit]

ericgibbs,

Interestingly your supporting diagram shows arrows indicating a direction of circular movement of the electrons around the circuit, so wouldn't you agree movement of electrons as shown in a continuous loop around the circuit suggests 'flow'.?? albeit an alternating current flow.??

Not AC with a battery, and not continously with respect to either time or circuit path. There is a time limit determined by how much accumulation/depletion can occur on the plates. Electrostatic induction is just another name for accumulation/depletion.

Also the text describes movement of 'electrons' on the plates,ie: an electron moving onto one plate and another electron moving out of the other plate, dont you consider that as current flow around the circuit path???

Accumulation current surely exists up to the dielectric. Then electrostatic induction, caused by the electric field in the dielectric, causes a depletion current to move from the opposite plate back around the loop. No charge carrier goes through the dielectric, only EM fields.

Ratch

 

[killivolt]

Ok, ok, ok. I got this now. Back on page one again.

killivolt,
Yes, current is moving to accumulate on one plate and deplete on another. I thought I stated that enough already. Why are you concerned with vibrating electrons and waves? The same thing happens in slowly changing DC.

Yes, I totally agree. I had this understanding, before I read the opening sentence in this thread. I felt prior to this my basic understanding was a static discharge with electrons flowing from plate to plate. It was the vacuum capacitor that made my mind stop and think about it. I was ok with Santa Claus being a real person till then.

There is an EM field from one plate to the other through the dielectric. It is caused by the imbalance of charge between the plates. You will never see the EM fields any more than you will "see" gravity fields. Why are you making it so complicated and difficult? Anytime charges are gathered together, an electrostatic field forms. The intensity of this field is proportional to the amount of charge gathered and how closely it is packed. During the process of gathering, the charge carriers have to physically move, so that makes a current. In a capacitor this current does not go past the dielectric. The change in the gathering charge also causes a change in the electrostatic field across the plates. This EM field change has a equivalency to current, but it is not physical current. It is called displacement current.

This along with the diagrams have returned me to an almost sane view of what I knew only clearer. I can agree with charge to charge imbalance "one in" and "one out" with a moving field energy between them. Only if the charge buildup is the movement needed to create the first EM pulse as Brownout said.

No one has said so before, but the displacement current is really just an example of electrostatic induction.Ratch

Finally I'm ok with this I think my mind is no longer thinking about the double slit experiment. Exellent example and Thank you for staying with me. I almost was lost in the cosmos.

Unless someone wants to put some more gin in my juice.

 

[Mr RB]

...
The pool 'wave' dosn't propagate, the surface displacement propagates across the surface of the pool.
A cork floating on the water would just bob up an down as the displacement wave passed by, it would not move along with the 'wave'
...

I got chills. With your one elegant paragraph analysing a water analogy it seems you have explained what "displacement current" is and also made a pretty good argument that it actually exists in some physical sense even though the water molecules (electons) do not themselves go "through" from the input to the output.

... You will never see the EM fields any more than you will "see" gravity fields. ...

You never played with iron filings and a bar magnet Ratchit? EM fields are VERY easy to see compared to "gravity fields".

... The change in the gathering charge also causes a change in the electrostatic field across the plates. This EM field change has a equivalency to current, but it is not physical current. It is called displacement current. ...

Nice to see you saying something smart for a change.

So we are all starting to agree on some points?
1. Displacement current exists in some physical sense between plate A and plate B but is not a "conducted" current of electrons between plate A to plate B.
2. The physical nature of displacement current is largely a property of electromagnetic field or electrostatic field, possibly some combination of both depending on capacitor type.
3. Displacement current must be equal to conduction current in the circuit (current into/out of plate A).

 

[Ratchit]

killivolt,

This along with the diagrams have returned me to an almost sane view of what I knew only clearer. I can agree with charge to charge imbalance "one in" and "one out" with a moving field energy between them. Only if the charge buildup is the movement needed to create the first EM pulse as Brownout said.

Why does the charge imbalance have to be a pulse? It can be a slow gradual buildup. Since it is assumed the plates of the capacitor are stationary with respect to each other, I would not say that the EM field is moving. It is increasing and decreasing yes, but not moving.

Mr RB,

You never played with iron filings and a bar magnet Ratchit? EM fields are VERY easy to see compared to "gravity fields".

No, you are seeing the effects of the EM field. The field itself is invisible. Just like you cannot see the wind, but you can see the waves on the water.

Nice to see you saying something smart for a change.

I have always said that the displacement current was a virtual current caused by the change in the E-field, and that accumulation/depletion made the current appear to pass through the capacitor. I have been consistent about that. I challenge you to show where I made an incorrect statement.

So we are all starting to agree on some points?
1. Displacement current exists in some physical sense between plate A and plate B but is not a "conducted" current of electrons between plate A to plate B.

Yes, the displacement current is an equivalance, but not an equality to the conduction current. It is caused by the changing EM fields in the dielectric.

2. The physical nature of displacement current is largely a property of electromagnetic field or electrostatic field, possibly some combination of both depending on capacitor type.

I would say that any capacitor regardless of the type would have an EM field in the dielectric, and support a displacement current.

3. Displacement current must be equal to conduction current in the circuit (current into/out of plate A).

For a series capacitor, yes. But for a conducting wire, the professor showed that the displacement current is very much smaller than the conducting current.

Ratch

 

[killivolt]

killivolt,Why does the charge imbalance have to be a pulse?

Because I can see the inference to the one time event. Not moving but a rise and fall as it should. The next will be in the exact place and will rise and fall.

It can be a slow gradual buildup.

This part I like the most and is even more clear. As long as electrons move. Yes. I don't care about time it's the movement as if they are slowly collected in what ever shape they want to be or even re-arrange. This is good stuff.

Since it is assumed the plates of the capacitor are stationary with respect to each other, I would not say that the EM field is moving. It is increasing and decreasing yes, but not moving.Ratch

No, problem. Even more clear.

 

[BrownOut]

The EM field does move, as do all fields. It would be absurd that it is the same in all space at the same time, under dynamic conditions.

 

[killivolt]

The EM field does move, as do all fields. It would be absurd that it is the same in all space at the same time, under dynamic conditions.

You just put the gin in my juice. I just stopped drinking that and now my vision has just gotten a little well ........... I'm seeing double again?

Edit: Anybody want a drink?

 

[Ratchit]

killivolt,

You just put the gin in my juice. I just stopped drinking that and now my vision has just gotten a little well ........... I'm seeing double again?

You shouldn't if you think about it. Static fields do exist, and by definition, they don't move. The plates of a capacitor anchor the two sources of the field. So even though the field inside of a capacitor can be dynamic, it does not move because its two source locations (plates) do not move with respect to each other. The flux changes, but the field does not move. If you plant a sapling, and 50 years later it grows into a tall tree, did the tree move?

Ratch

 

[killivolt]

killivolt,



You shouldn't if you think about it. Static fields do exist, and by definition, they don't move. The plates of a capacitor anchor the two sources of the field. So even though the field inside of a capacitor can be dynamic, it does not move because its two source locations (plates) do not move with respect to each other. The flux changes, but the field does not move. If you plant a sapling, and 50 years later it grows into a tall tree, did the tree move?Ratch

Now that's a number I can understand. For the moment I am just about to hit the ceiling,

Thank you Brownout. I'm not done yet until I see the litmus Paper. But, I can for now conclude the daunting measure of how a capacitor works.

 

[ericgibbs]

ericgibbs,
Not AC with a battery, and not continously with respect to either time or circuit path. There is a time limit determined by how much accumulation/depletion can occur on the plates. Electrostatic induction is just another name for accumulation/depletion
Accumulation current surely exists up to the dielectric. Then electrostatic induction, caused by the electric field in the dielectric, causes a depletion current to move from the opposite plate back around the loop. No charge carrier goes through the dielectric, only EM fields.
Ratch

You are missing the point of my missive,

The point I was 'trying' to make is that you and your supporting link, have to to resort to the 'incorrect', out of date, conventions of displaying and describing the flow of electronics thru a circuit, in order to try to explain your way of seeing current as 'existing' and not flowing.

As I recall, when I close a switch that connects a battery to a capacitor, [in a loop circuit], the leading edge of the voltage/current pulse applied to the capacitor will pass thru the capacitor and appear on the other side of the capacitor as a differentiated pulse.

I dont know why, when you reply to posts, you starting trying to explain points which have not been mentioned by the poster.????

No where in my post have I mentioned.
There is a time limit determined by how much accumulation/depletion can occur on the plates.
Electrostatic induction is just another name for accumulation/depletion
Accumulation current surely exists up to the dielectric.
Then electrostatic induction, caused by the electric field in the dielectric, causes a depletion current to move from the opposite plate back around the loop.
No charge carrier goes through the dielectric, only EM fields.

Please dont pad out your posts...