Capacitance in Series: Questions for David

[Firefox123]

Hello again David...

Russ,

O.K. Now that we are in agreement on what is going on in the circuit. There are some additional questions I have that I don't fully understand. I'm not sure if you know that answers or not either. However, here they are.

1). In the following region. I put numbers in for easier reference.

BATT ***wire*** CAP 1 *****wire***** CAP 2******wire*** BATT
1- ______2______ 3- 4+(5-) ____6______ 7- 8+(9-) ____10_____ 11+

Okay...

1). Where is the boundary of 4+ to (5-)? Is it right at the cap to wire boundary or does positive charge extend past the plate and move into the wire. I'm envisioning that positive charge starts to push down the wire with increasing battery voltage.

I would say that all of the electrons (and lack thereof) are all physically on the plate itself in this interface. I doubt that we ever have a case where the "lack" of electrons extends into the wire. (think about how many electrons are on thsoe capacitor plates!)

2). Are electrons evenly distributed from the points of (5-), 6, 7- region? Or is there a gradient from (5-), 6, 7-? If there is a gradient, I'm assuming that maximum amount of electrons are at 7- and the least amount is at (5-).

I thought there might be a gradient at first also, but after further thought I believe the electrons in the wire in between distribute themselves basically how they would on any conductor in electrostatic equilibrium. They try to get as far from each other as possible and are basically "evenly" distributed.

3). On all wires in the circuit, I'm assuming that all charge reside on the surface of the wire. Do you believe this to be true? Is this also true for the electrons in the (5-), 6, 7- region?

The actual electrons that are part of the wire itself are actually throughout the wire, not just on the surface...remember the rule is that any excess charge placed on a conductor in static equilibrium resides on the surface of the conductor.[/color]

"Excess" here means charge not associated with the material itself.

4). For the Q = CV equation. Is Q just the electrons that reside on the capacitors plates or does it include charge that reside in the wires as well. I'm expecially interested if this is the case in the (5-), 6, 7- region?

Q=CV is referring to the charges on the capacitor only.

Sorry I have more questions than answers. Let's stop here and see what you have to say.

No problem.



Russ

 

[meldave00]

Russ,

Sorry I have not been able to get on here as of late. But if you don't mind I would like to bombard you with a few more questions.

Again, I am inserting our text capacitor circuit for reference.

BATT ***wire*** CAP 1 *****wire***** CAP 2******wire*** BATT
1- ______2______ 3- 4+(5-) ____6______ 7- 8+(9-) ____10_____ 11+

Question 1.
Pretty much all physics books and electronic books say the same thing for capacitors in series. Assume Q1neg = Q1pos = Q2neg = Q2pos. Where Q's are referring to the number of charge. First, do you agree with what the books are saying? Second, can you comment on exactly what areas of our text capacitor circuit this is implying? I haven't forgotten about your explanation of capacitors in series, however I am now trying to link your thoughts to what the textbooks are saying.

Question 2.
Do you think that it is true that the battery can only expel an electron from its negative terminal if an electron is sucked into its positive terminal. Than is, no electron can leave the battery without some available to enter?

Question 3.
Let's imagine this circuit. Single capacitor circuit.
BATTneg ***wire*** CAP 1 ******wire*** BATTpos.
If you care to, please try to describe all the Efields in the circuit when the circuit is in equilibrium. From what I understand, the only Net Efield exists from the positive plate to the negative plate of the capacitor. However, there are additional Efields extending out into the wires and such that are canceled out. The attached picture (click to enlarge) shows the Efield of two plates that have positive and negative charge respectively. It shows two Efields going out from both sides of the positively charged plate and shows two Efield coming in from both sides of the negatively charged plate. If shows that on the outsides of each plate that the positive and negative Efields cancel each other, but do not cancel each other between the plates. This to me makes sense. However, this is the case where an opposite Efield from one plate extends passed the outer side of another plate and cancels out the plate to wire Efield of the plate it extended passed. My question is... what happens if we stick a battery across these plates that introduces it own Efield

regards,

David

 

[Firefox123]

Hi david...

Just wanted to let you know that I did see your last post and I am planning on answering it tomorrow if time permits.

Till then.



Russ

 

[Firefox123]

Russ,

Sorry I have not been able to get on here as of late. But if you don't mind I would like to bombard you with a few more questions.

Hi David. Bomb away.

Again, I am inserting our text capacitor circuit for reference.

BATT ***wire*** CAP 1 *****wire***** CAP 2******wire*** BATT
1- ______2______ 3- 4+(5-) ____6______ 7- 8+(9-) ____10_____ 11+

Question 1.
Pretty much all physics books and electronic books say the same thing for capacitors in series. Assume Q1neg = Q1pos = Q2neg = Q2pos. Where Q's are referring to the number of charge. First, do you agree with what the books are saying? Second, can you comment on exactly what areas of our text capacitor circuit this is implying? I haven't forgotten about your explanation of capacitors in series, however I am now trying to link your thoughts to what the textbooks are saying.

Yes. I do agree that the 'Q's are the number of charges on the plates.

As far as the areas go let's look at areas 3,4,5 and 7,8,9. Since these are basically the same setup what we can conclude about 3,4,5 applies to 7,8,9.

Imagine an electron is removed from + plate (region 4) and that same electron is then placed on - plate (region 3). Where will this extra electron reside (I specifically say "extra" here because this electron is not a part of the orignal electrons that make up the negative metal plate, it was added to - plate {region 3} and removed from + plate {region 4}) This electron will reside on the outer surface of the - plate.

On the + plate we are missing an electron so there is a "net positive" voltage. This happens for many electrons on the plates.

Even when we are in an electrostatic equilibrium and no current is flowing the negative charge from the - plate still repels electrons from the + plate. So we get a separation of charge on the + plate. Keep in mind though that the + plate is still positively charged overall despite any charge separation.

Question 2.
Do you think that it is true that the battery can only expel an electron from its negative terminal if an electron is sucked into its positive terminal. Than is, no electron can leave the battery without some available to enter?

Im not sure to be honest...Im sure we could imagine a hypothetical situation where an electron could leave the negative terminal and not get replaced. But hypotheticals aside, a battery has internal chemistry that is maintaining the voltage across the terminals and is allowing an electron to "leave" the negative terminal while the positive terminal "accepts" an electron. You might want to read up on how batteries work.

Question 3.
Let's imagine this circuit. Single capacitor circuit.
BATTneg ***wire*** CAP 1 ******wire*** BATTpos.
If you care to, please try to describe all the Efields in the circuit when the circuit is in equilibrium. From what I understand, the only Net Efield exists from the positive plate to the negative plate of the capacitor. However, there are additional Efields extending out into the wires and such that are canceled out. The attached picture (click to enlarge) shows the Efield of two plates that have positive and negative charge respectively. It shows two Efields going out from both sides of the positively charged plate and shows two Efield coming in from both sides of the negatively charged plate. If shows that on the outsides of each plate that the positive and negative Efields cancel each other, but do not cancel each other between the plates. This to me makes sense. However, this is the case where an opposite Efield from one plate extends passed the outer side of another plate and cancels out the plate to wire Efield of the plate it extended passed. My question is... what happens if we stick a battery across these plates that introduces it own Efield
View attachment 7342

Could you give me the site where you got that diagram from? Id like to see how they are describing the figure..

Anyway...I think I understand what the E-fields in the figure are and it looks okay to me.


Okay for a single capacitor circuit with a battery connected to it.

A battery is kind of like a capacitor in a way, just that a battery has interal chemistry that maintains the voltage across it while a capacitor does not.

In equilibrium we have an electric field across the battery terminals and an electric field across the capacitor plates. Those two electric fields cancel each other out such that neither the capacitor nor the battery can move any electrons. They are both pushing electrons with equal force, but in opposite directions, within the wire so nothing moves.


Does that make sense?




Russ

 

[meldave00]

Russ,

Thanks for the response. I will respond later when today when I have more time.

David

 

[satbin]

what is the fringe field of the capacitor. I was reading a book Electric and Magnetic Interactions by Ruth Chabay and Bruce Sherwood and they say fringe field of capacitor cancels the field due to battery and surface charges in a single cap. and battery circuit. I can scan the page from the book if you want to see.

thanks