AC Current Flow Question

[RayS]

well, I'd like to add a different view. I voted current thru 2 would be greater.

Since we are talking electrostatic only, you are basically just charging one or the other, and since the ground has a much higher capacity to store a charge, i think more current would flow there.

Imagine if the circuit was built using 2 different spheres, one much larger than the other. Assume no coupling between the spheres. You would have minute charging/discharging flows to each, but more toward the bigger one.

 

[weressl]

well, I'd like to add a different view. I voted current thru 2 would be greater.

Since we are talking electrostatic only, you are basically just charging one or the other, and since the ground has a much higher capacity to store a charge, i think more current would flow there.

Imagine if the circuit was built using 2 different spheres, one much larger than the other. Assume no coupling between the spheres. You would have minute charging/discharging flows to each, but more toward the bigger one.

But we are NOT talking electrostatic charge. We are talking about an AC voltage source and capacitive coupling.

 

[RayS]

But we are NOT talking electrostatic charge. We are talking about an AC voltage source and capacitive coupling.

I am talking electrostatic- the fact that it is AC is what enables the current to keep flowing- it charges positive, then negative....

don't ask me what the actual currents would be, all I would say is...small.

 

[weressl]

I am talking electrostatic- the fact that it is AC is what enables the current to keep flowing- it charges positive, then negative....

don't ask me what the actual currents would be, all I would say is...small.

You can talk all you want it still is NOT electrostatic. The charge transfer would NOT show up on an ordinary ammeter.

It is an AC circuit and as it was pointed out the two ammeters are in series, so they must show the same current.

 

[RayS]

You can talk all you want it still is NOT electrostatic. The charge transfer would NOT show up on an ordinary ammeter.

It is an AC circuit and as it was pointed out the two ammeters are in series, so they must show the same current.

-nope, ordinary ammeter won't show it as this is just electrostatic :grin:
gotta pull out the electron counter for this one (coming soon from wishful electrostatics, inc.)
- I think the ammeters being in series=same flow was the original question, and since there is an AC circuit, there may well be different flows in the 2 branches. I see 3 different paths- 1 path capacitively coupled from the plate to earth, 1 from xfmr to plate "static" and 1 from plate to ground "static".

I think flow across a capacitor is in essence electrostatic.
View attachment 1287

 

[weressl]

-nope, ordinary ammeter won't show it as this is just electrostatic :grin:
gotta pull out the electron counter for this one (coming soon from wishful electrostatics, inc.)
- I think the ammeters being in series=same flow was the original question, and since there is an AC circuit, there may well be different flows in the 2 branches. I see 3 different paths- 1 path capacitively coupled from the plate to earth, 1 from xfmr to plate "static" and 1 from plate to ground "static".

I think flow across a capacitor is in essence electrostatic.
View attachment 1287

Even though your circuit diagram is wrong. The ammeters are in the same circuit therefore they do read the same.

Static means : NOT MOVING, therefore there is no flow.....it is a capacitive charge and discharge.

Transformer has two legs:
H1 leg connected to the insulated body - one plate of the capacitor
H2 leg is connected to ground - second plate of the capacitor.
The dielectric in this case is air that is between the two plates. (Of course the earth itself provides sime of the capacitance, as nothing is of pure one thing or the other.)

The flow from H1 to H2 is the only circuit that is there so the current is the same in both ammeters.

 

[crossman]

Weressl:

Just to make sure I am thinking correctly:

I am in agreement that in an AC circuit with a capacitor, the Physics texts refer to the field as an "electric field" rather than an "electrostatic" field. In my previous posts, I wrongly used the term "electrostatic field" where I should have just used "electric field."

The electric field is a field which can be described by lines of force extending from the positive charge and pointing to the negative charge. As the AC voltage is applied to the capacitor, the "electric" field reverses directions along with the reversal of polarity on the plates.

If we replace my use of "electrostatic field" with "electric field," then my argument still holds.

Does all that sound reasonable?

 

[RayS]

Even though your circuit diagram is wrong. The ammeters are in the same circuit therefore they do read the same.

Static means : NOT MOVING, therefore there is no flow.....it is a capacitive charge and discharge.

charge and discharge involves current flow does it not?
the ammeters are in the same circuit, but in different branches. Impedance to ground is different. Imagine removing the ground connection in my schematic- does anything happen? if there is any change, there must be current flow. If there is current flow, it will not be the same on both branches.

edit to clarify

 

[RayS]

question: if we replace the plate in the original post with an antenna- is the energy radiated due to electrostatic coupling?

granted you don't get much output at line frequency...

 

[crossman]

question: if we replace the plate in the original post with an antenna- is the energy radiated due to electrostatic coupling?

My guess is that at 60Hz, the antenna is going to do nothing but act as one plate of a capacitor. Perhaps I am missing something. Is there something special about an antenna as compared to a chunk of metal when we are discussing 60 cycles?

Edit: typo

 

[jghrist]

question: if we replace the plate in the original post with an antenna- is the energy radiated due to electrostatic coupling?

granted you don't get much output at line frequency...

If you are talking about a radiated field, it is an electromagnetic field, not an electric field or a magnetic field. The antenna would not be very effective unless it were at least a quarter wavelength long (a few hundred miles).

 

[RayS]

crossman- nothing special about the antenna, just helps me visualize it.
jghrist- agreed on the wavelength

im just thinking outside the box (or circuit) here. I don't think the xfmr leakage current has to flow around the loop thru both ammeters. I see it as more of a coil to case potential, not necessarily tied to the secondary terminals.

It's an interesting question.

 

[crossman]

Please bear with me as my obsession for this topic has not quite subsided. I am submitting one more graphical explanation for those who may still feel that capacitance is not the major mechanism allowing current to flow onto or off of the conducting body.

In this idealized experiment, the source is AC. I will examine a given 1/4 cycle. Leakage current through air is negligible.

The point is that in this experiment, the current flow in the circuit is intimately tied to the charactaristics of both the conductive body and the earth. Together, these form a capacitor which is the mechansim which allows current to flow. I see no other mechanism which would allow current to flow onto the conductive body other than capacitance.

In fact, the very definition of capacitance itself was developed by the physicists to exactly account for the phenomenon we are demonstrating.

Comments welcomed.

 

[Krim]

I'm with Charlie. The current flowing through the loop is the same all the way around the loop. If meter 1 is somehow reading 60 mA, then so is meter 2.

In addition, I would have to say that unless you draw in an arc from the conductive body to earth, you don't have any current flow at all. :smile:

That was my first thought, how can ammeter 1 read anything without the conductive body being grounded ? I simply voted 0 due to the unknown factors.

 

[zog]

That was my first thought, how can ammeter 1 read anything without the conductive body being grounded ? I simply voted 0 due to the unknown factors.

Because this drawing and this discussion was brought into this thread from another thread where we were discussing HV systems

 

[zog]

Please bear with me as my obsession for this topic has not quite subsided. I am submitting one more graphical explanation for those who may still feel that capacitance is not the major mechanism allowing current to flow onto or off of the conducting body.

In this idealized experiment, the source is AC. I will examine a given 1/4 cycle. Leakage current through air is negligible.

The point is that in this experiment, the current flow in the circuit is intimately tied to the charactaristics of both the conductive body and the earth. Together, these form a capacitor which is the mechansim which allows current to flow. I see no other mechanism which would allow current to flow onto the conductive body other than capacitance.

In fact, the very definition of capacitance itself was developed by the physicists to exactly account for the phenomenon we are demonstrating.

Comments welcomed.

What makes you think the electons need to go through ground? They will jsut return to the source through several paraell paths including a path directly back to the transformer bypassing your Ammeter#2. Therefore AM#2 will read slightly less than AM#1.

 

[hardworkingstiff]

This post is being taken out of context, please read posts 1-334 of "current retuning to a different source" thread.

Right, :smile: :grin:

 

[charlie b]

What makes you think the electons need to go through ground?

Because it is one half of the capacitor, and because planet Earth is a very good conductor.

They will just return to the source through several parallel paths including a path directly back to the transformer bypassing your Ammeter#2. Therefore AM#2 will read slightly less than AM#1.

Electrons are not going to jump off the "conducting body," fly through the air, and land on the transformer. Unlike planet Earth, air is a very poor conductor. There is no parallel path.

The current leaving the transformer (and passing through AM#1) is, shall be, and must be the same as the current entering it (and passing through AM#2).

 

[RayS]

Crossman, I think that you have illustrated classical AC flow thru a capacitor.
I agree with the statement in frame 6 of the requirement to have capacitance to have this flow.

What I would like to add is
- that the current could flow even without the interaction between the conductive body and the earth described by the electric field lines in frame 6.
Heres my logic- just by virtue of having mass both the earth and the conductive body can receive charges- this is the origin of capacitance, the capacity to hold a charge. Since this is AC, the charge/reverse charge cycles will cause a current flow by literally moving electrons on and off the earth and the conductive body. Think old fashioned leyden jar or electrometer, both nicely described on the Wikipedia site.
- current in a separate circuit will also flow due to parasitic capacitance from the windings. I don't believe this flow will necessarily be tied to the xfmr secondary terminals.

This is a great question, and I appreciate the brain power being expended. I credit your "obsession" as being determination to increase understanding, it is helping mine. I havent' finished reading the other thread yet, but intend to. Thanks!

 

[coulter]

zog][/b]This post is being taken out of context, please read posts 1-334 of "current retuning to a different source" thread.

Right, :smile: :grin:

Nope. I read the first few pages when it got started - enough to see it disintegrate into two camps. One trying to discuss a math model, the other discussing the practical difficulties of measuring this at 60kv.

Crossman wants to discuss physics/math models. I don't see this as out of context for this thread.

carl