Charge Buildup & Equalization on Batteries A & B

[Evil Bunny]

The other thread was getting messy... Starting fresh again:

We have two batteries. Let's say they are fully charged at 12Volts. We'll call them battery A and battery B.

Is there a buildup of negative charge on the (-) pole of these batteries and a buildup of positive charge on the (+) poles?

If there is... and we connect the (-) pole of battery A to the (+) pole of battery B (nothing connected to the other terminals), why is there no current flow? Why is completing the circuit necessary for these charges to equalize?

If there is not a buildup of charge on the terminals... why not?

 

[daumphys]

This site is useful to you.
http://en.wikipedia.org/wiki/Lead–acid_battery
Seeing this site, you could know how it works.

 

[Studiot]

Is there a buildup of negative charge on the (-) pole of these batteries and a buildup of positive charge on the (+) poles?

No

If there is... and we connect the (-) pole of battery A to the (+) pole of battery B (nothing connected to the other terminals), why is there no current flow?

Why should there be flow since you have provided nothing for it to flow through?

Why is completing the circuit necessary for these charges to equalize?

Thre are no charges to equalise.

Batteries do not work like this. Like the Man says, read the Wiki.

You can also learn by simply reading what others have already written as well as by asking questions.

 

[Evil Bunny]

Is there a buildup of negative charge on the (-) pole of these batteries and a buildup of positive charge on the (+) poles?

No.

Why not?

Edit: and the link is broken (or my computer is)

 

[xxChrisxx]

Just type battery into wiki.

 

[shoestring]

Is there a buildup of negative charge on the (-) pole of these batteries and a buildup of positive charge on the (+) poles?

The important thing is that there is a voltage difference between the poles. That could mean that one of them is negatively charged and the other positively charged, but you'd also get a voltage difference if one had a small negative charge and the other a big negative charge (or a small and a big positive charge) or if one was neutral and the other charged.

If you connect two batteries like that, the negative pole of one battery connected to the positive pole of the other, but the circuit kept open, I imagine that some equilibrium would soon be reached. That could involve a short-lived current just to redistribute charges, but once equilibrium is reached the current would end.

I think there is, in general, at least a small charge on the poles of the batteries, created and sustained by the chemical reactions in the battery.

 

[shoestring]

Just a though: If each battery has a voltage of 1.5 V, then the voltage difference between the free poles of the connected batteries shoud be 3.0 V. The higher voltage difference should correspond to a higher "charge difference" between the free poles, for example by a bigger negative charge on the free negative pole, and a bigger positive charge on the free positive pole, compared to before the batteries were connected.

Edit: Once equilibrium is reached for the open circuit with the connected batteries, I imagine that the field from the more heavily charged free poles will counteract any field from the connected, and probably less charged, poles. The end result would be no further current in the conductor joining the the two connected poles.

 

[Evil Bunny]

Just type battery into wiki.

didn't answer the question posed.

 

[Studiot]

created and sustained by the chemical reactions in the battery.

Not by a build up of charge.

 

[shoestring]

Not by a build up of charge.

What else do you think happens at the electrode reactions? They add electrons to the electrode on one side, and take electrons from the electrode on the other side. The process doesn't start when the circuit is closed, it has already built up a voltage difference before the circuit is closed.

The electric field in and around the battery clearly doesn't come from a time-varying magnetic field in the case of a simple DC curcuit powered by a battery. What else can the elctric field come from? Answer: From the charge distribution. Where are those charges, in your opinion? A voltage difference implies that there's an electric field, because if E is zero everywhere, then there's no gradient of the potential, and then there's no voltage difference.

 

[xxChrisxx]

didn't answer the question posed.

That's because the questions aren't how batteries work.

 

[Studiot]

What else do you think happens at the electrode reactions? They add electrons to the electrode on one side, and take electrons from the electrode on the other side. The process doesn't start when the circuit is closed, it has already built up a voltage difference before the circuit is closed.

The electric field in and around the battery clearly doesn't come from a time-varying magnetic field in the case of a simple DC curcuit powered by a battery. What else can the elctric field come from? Answer: From the charge distribution. Where are those charges, in your opinion? A voltage difference implies that there's an electric field, because if E is zero everywhere, then there's no gradient of the potential, and then there's no voltage difference.

Both in this thread and bunny's other thread there seems to be considerable confusion between voltage and charge.

As soon as a single electron is exchanged at the elctrode, the full electrode potential is available. However the charge 'build up' is negligable.
A battery maintains this voltage by allowing the chemical reaction to proceed, as current (charge) is demanded of it. The whole charge that the battery can supply is not available as 'built up charge' at anyone time.

Exactly as stated in the quote by yourself.

 

[rcgldr]

The terminals of a battery will have a small charge on them, but unlike a capacitor, without the chemical reaction that occurs when current flows within the battery, the effective resistance between the terminal and internals of the battery goes to near infinity as soon as any charge is added or removed from one of the terminals.

 

[Drakkith]

Bunny, there isn't a buildup of charge on one terminal because of the way a battery works. The chemicals in a battery don't have a net positive or negative buildup of charges. Instead, they have different electron affinities. When you close the circuit it allows a chemical reaction to take place between the electrolytes and the electrodes. The negative side loses an electron in this reaction, which then allows the positive side to gain an electron in the reaction. Without the circuit being closed, you might get a couple of reactions and then they would stop. There's no way for electrons to get to the other side, so the chemical reactions can't continue.

 

[Evil Bunny]

Okay, I get it now with the battery... the chemical reactions cannot continue.

Now what about a generator. I'm assuming there is also no "charge" on the pole of a generator either. What prevents the buildup of charge on a pole of a generator if it's not a chemical reaction?

 

[Drakkith]

Okay, I get it now with the battery... the chemical reactions cannot continue.

Now what about a generator. I'm assuming there is also no "charge" on the pole of a generator either. What prevents the buildup of charge on a pole of a generator if it's not a chemical reaction?

As I said in the other thread, the electrons try to move, but since there are no "replacement" electrons, positive ions cause an opposite force to develop that equals the charge of the generator that keeps the electrons from building up anywhere. Hence you need to complete the circuit to have somewhere for the electrons to go to/ come from.

 

[shoestring]

Not by a build up of charge.

By build up of a charge I meant up to a point, not a continuous build up forever. The build up will halt when the potential difference between the poles has been achieved.

 

[xxChrisxx]

By build up of a charge I meant up to a point, not a continuous build up forever. The build up will halt when the potential difference between the poles has been achieved.

I normally hate it when people do this needlessly but.
Do you have any evidence to back that statement up?


Batteries do not build up charge becuase the electricity flows. It marks the very difference between a static charge and flowing charge. I think it was pointed out earlier, this is the reason the full potential is available the instant you make a circuit,not after it builds up for a bit.

 

[shoestring]

I normally hate it when people do this needlessly but.
Do you have any evidence to back that statement up?


Batteries do not build up charge becuase the electricity flows. It marks the very difference between a static charge and flowing charge. I think it was pointed out earlier, this is the reason the full potential is available the instant you make a circuit,not after it builds up for a bit.

I believe the potential is built up in a short time, and that it happens before the battery is connected to a circuit. I believe the closed circuit has both flowing charges and a static surface charge distribution. With a current in the wires, there'll be an electric field along the wire, because the wires aren't resistance free. The field may be small, if the resistance is small, but it's there, driving the current. That field must be derived from some charge distribution, or the field wouldn't be there.

I don't think there's anything mysterious about the potential difference between the poles of a battery. I think it is related to charges on the poles, because I can't think of any other possible explanation for it. To me it'd be contradictory to say that there are no charges on the poles, but there's a voltage, i.e. a potential difference between the poles. To me that's what requires an explanation: how there could possibly be a voltage without the charges.

 

[xxChrisxx]

I believe the potential is built up in a short time, and that it happens before the battery is connected to a circuit. I believe the closed circuit has both flowing charges and a static surface charge distribution. With a current in the wires, there'll be an electric field along the wire, because the wires aren't resistance free. The field may be small, if the resistance is small, but it's there, driving the current. That field must be derived from some charge distribution, or the field wouldn't be there.

Unfortunately, what you believe is irrelevent.
This phenomana just isn't obvserved at battery teminals.

If you can find somewhere credible that says it does, please feel free to post it.

I don't think there's anything mysterious about the potential difference between the poles of a battery. I think it is related to charges on the poles, because I can't think of any other possible explanation for it. To me it'd be contradictory to say that there are no charges on the poles, but there's a voltage, i.e. a potential difference between the poles. To me that's what requires an explanation: how there could possibly be a voltage without the charges.

Read up on half cells. It's the chemical reaction that has a certain potential. When you put the two half cells together you get a battery.

This is the reason why lemons can work as batteries with two different electrodes.



I'd also like to point you to the foum guidelines on personal theories and explinations.
https://www.physicsforums.com/showthread.php?t=414380

Overly Speculative Posts:
One of the main goals of PF is to help students learn the current status of physics as practiced by the scientific community; accordingly, Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums or in blogs, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion.

 

[shoestring]

Unfortunately, what you believe is irrelevent.
This phenomana just isn't obvserved at battery teminals.

If you can find somewhere credible that says it does, please feel free to post it.

Charges aren't visible, so they're not that easy to observe! Really, how would you directly observe a charge responsible for a potential of, say, 1.5 V? Nothing wrong with relying on logic and deduction rather than direct observation, I think. I will, however, look for credible sources backing up the statement.

Read up on half cells. It's the chemical reaction that has a certain potential. When you put the two half cells together you get a battery.

I think the chemical reaction creates the potential. The electrochemical electrode reaction is energetically favorable up to the point where so many charges have accumulated on the electrode that it costs as much as it pays to continue with the reaction. That happens when the electrode has a certain potential relative to the solution.

I'd also like to point you to the foum guidelines on personal theories and explinations.
https://www.physicsforums.com/showthread.php?t=414380

Apologies if have been sloppy in backing up every statement with a credible source. Still, it's hardly any obscure novel theories I'm referring to, but fairly mainstream reasoning about charges, fields and potentials.

Thorough research to find sources takes time, which I don't always have enough of, so I've tried to use expressions like "I suppose", "probably" etc. in order not to pose as more of an expert than I am.

BTW, have you found any credible sources claiming that there are zero charges on the poles of a battery? Or is that so obvious to you that there's no need for it?

 

[shoestring]

If you can find somewhere credible that says it does, please feel free to post it.

Here's a link to a page from the http://www.qrg.northwestern.edu/" at Northwestern University that states that there's a build-up of electrons at the anode:

http://www.qrg.northwestern.edu/projects/vss/docs/power/2-how-do-batteries-work.html"

A direct quote from the page:

The chemical reactions in the battery causes a build up of electrons at the anode.

 

[Studiot]

This has more authority

https://www.physicsforums.com/archive/index.php/t-244308.html

 

[shoestring]

This has more authority

https://www.physicsforums.com/archive/index.php/t-244308.html

Ok, but when xxChrisxx asked for somewhere credible, I didn't realize that physicsforums.com counted as more credible than Northwestern University. My bad, I'm sorry!

 

[Studiot]

There are actually quite a few things wrong the the NWU description of a battery, but what do you expect from what appears to be the parapsychology department.

Ghostbusters anyone.

 

[Evil Bunny]

As I said in the other thread, the electrons try to move, but since there are no "replacement" electrons, positive ions cause an opposite force to develop that equals the charge of the generator that keeps the electrons from building up anywhere. Hence you need to complete the circuit to have somewhere for the electrons to go to/ come from.

Ok... Let's try this again... You're saying that as electrons try to leave the (let's say) negatively charged wire of the generator, the "leaving" electrons are creating positive ions by moving away from their protons, which creates an equally positive charge on these atoms that attracts the electrons back to them?

This doesn't make sense to me because the whole reason that there is a negative charge to begin with is because there are too many electrons to be attracted to the "deficiency" of protons on the wire... If there are "extra" electrons (which makes the "charge" negative, right?), why aren't they attracted to the earth, which has less "extra" electrons (less negative charge, more available protons to accept them)?

 

[Drakkith]

This doesn't make sense to me because the whole reason that there is a negative charge to begin with is because there are too many electrons to be attracted to the "deficiency" of protons on the wire... If there are "extra" electrons (which makes the "charge" negative, right?), why aren't they attracted to the earth, which has less "extra" electrons (less negative charge, more available protons to accept them)?

In your generator there isn't a negative charge. The negative terminal of the generator isn't at a negative charge like a door handle or your hand would be in the case of static electricity. The generator is exerting a force on the electrons, but since they have nowhere to go no charge builds up. The generator doesn't produce extra electrons, and it doesn't have an inbalance in charges either. When the circuit is completed the electrons now have a path to circulate and the generator produces electrical power. If you shutdown your generator you have not more force and therefore no more electricity will flow. Note that this is a circulation of charges, not a redistribution to balance them out.

A generator is using the magnetic force to make electrons move in a conductor. A battery or capacitor is using the difference in electric charge instead.

 

[willem2]

I don't understand all of this.
- there will be charges on the anode and cathode of a battery, there must be, because there is an electric field.
- These charges are very tiny, because the capacitance between the poles of a battery is only a few pF.

 

[xxChrisxx]

I don't understand all of this.
- there will be charges on the anode and cathode of a battery, there must be, because there is an electric field.
- These charges are very tiny, because the capacitance between the poles of a battery is only a few pF.

What don't you understand there, as that seems right to me.
EDIT: Or is it just the thread you don't understand?

Also:

Here's a link to a page from the Qualitative Reasoning Group at Northwestern University that states that there's a build-up of electrons at the anode:

http://www.qrg.northwestern.edu/proj...ries-work.html

A direct quote from the page:

That is an overly simplistic description of a battery to the point of being wrong. It's more how you would describe it to someone in year 9 science than university.

I'll try to get together a description and some links as to the processes at work. From there hopefully you'll see why an equivalent to a 12V static charge doesn't build up between the terminals of a car battery.

You'll have to bear with me as this will take quite a while to construct a decent post. I may even just break each concept up into a separate post.


EDIT: I've tried thinking about this and I don't know where to start trying to explain it.

I can't understand why you think charges would build up at a pole when they are attached to a conductor.
Electrons in a cell can only be procuded when both sides of the cell are connected by a conductor.
So electrons cannot build up anywhere, as soon as they are produced they flow. The voltage depends on how much/quickly electons are produced, which is determined by the metal used as the electrode and the electrolyte in the half cell.

I suppose a way of putting it (if you are familiar with production methods) are electricity is made 'Just in time'.
http://en.wikipedia.org/wiki/Just-in-time_(business )

They aren't made by the reaction and then stored in a warehouse (the poles of the battery) ready for movement. The instant they are made they are transported along the conductor.


I don't know if you acutally don't understand what's going on in a battery, or if you do understand and are trying to describe what's going using a static electric analogy (which doesn't really reflect reality).

 

[shoestring]

That is an overly simplistic description of a battery to the point of being wrong. It's more how you would describe it to someone in year 9 science than university.

Here's a paper at a more academic level:

http://ajp.aapt.org/resource/1/ajpias/v64/i7/p855_s1?isAuthorized=no"

written by the same J. D. Jackson who has written a well known book on electromagnetism (https://www.amazon.com/dp/047130932X/?tag=pfamazon01-20). It should count as a very credible source.

A quote from the abstract:

The significance of the surface electric charge densities associated with current‐carrying circuits is often not appreciated. In general, the conductors of a current‐carrying circuit must have nonuniform surface charge densities on them (1) to maintain the potential around the circuit, (2) to provide the electric field in the space outside the conductors, and (3) to assure the confined flow of current. The surface charges and associated electric field can vary greatly, depending on the location and orientation of other parts of the circuit.

Not sure if it mentions the charges on the poles of the battery specifically, but it makes clear that there are surface charges shaping the field in and around the circuit, closed or not, and because the poles of the battery are part of the circuit, I'd say it supports the idea of charges on the poles.

I think a battery should be tought of as a dipole. The chemical reactions push the electrons toward one pole, making the battery into an electric dipole. A disconnected battery can be a dipole without there being a current.

 

[Evil Bunny]

The generator is exerting a force on the electrons, but since they have nowhere to go no charge builds up.

They have all kinds of places to go. The issue at hand is that they only want to go to one place. Back to the "return" of the generator. The question is why? It doesn't have anything to do with charge, apparently... You started to talk about positive ions exerting an opposite force. That sounded almost like it had to do with charge, so I'm still missing something.

It has been explained repeatedly and in many different ways that a circuit must be completed. This much I do understand. What I don't understand is why... I thought the whole reason an electron ever moved in the first place was because of a "charge" or a "force" being exerted onto it.

 

[Evil Bunny]

When you have a dry lead acid battery, fresh out of the box... it's useless. No voltage.

When you add the acid to it, what happens?

Does the word "charge" enter the picture at all here?

 

[Dadface]

If you take two parallel metal plates and use connecting wires to join the plates to the poles of a battery then you will have a capacitor that charges exponentially with time. There will be a negative charge build up on the plate connected to the negative pole of the battery and a positive charge build up on the opposite plate.If now the wires are kept in place but the metal plates are removed then you still have a capacitor but of a much smaller capacitance.The charge which is now mainly stored on the ends of the wires will be correspondingly smaller.If the wires are now removed you will still have a capacitor but this time the poles of the battery itself constitute the plates.The charge stored can be calculated from Q=CV where C is the effective capacitance of the battery poles.

 

[Evil Bunny]

If you take two parallel metal plates and use connecting wires to join the plates to the poles of a battery then you will have a capacitor that charges exponentially with time. There will be a negative charge build up on the plate connected to the negative pole of the battery and a positive charge build up on the opposite plate.

What if you only used one plate and connecting wire on (pick a pole, any pole). Would a charge build up on it?

If not, why not?

 

[Dadface]

What if you only used one plate and connecting wire on (pick a pole, any pole). Would a charge build up on it?

If not, why not?

You could have any arrangement at all.If changes are made then the capacitance changes also and this will result in a redistribution of the charge build up.

 

[shoestring]

Here's how I think it works:

At equilibrium each pole will have a certain potential relative to the electrolyte. For example, if the equilibrium potential difference between the pole and electrolyte happens to be 1V, then it "costs" 1 eV to transfer an electron from higher to lower potential. The reason the potential is built up despite this "cost" is that there is a simultaneous release of (in this case) 1 eV from the chemical reaction that transfers an electron from higher to lower potential.

Any conductor attached to the pole is, in a way, like an extension of the pole. At least in the sense that it gets the same potential as the pole, as long as there's no significant voltage drop due to the current when the circuit is closed.