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There is an explanation of how a battery works that says that inside the battery, the electrons do a complete loop and can return to their starting point. When the electrons arrive in the positive terminal and they lost all of their potential energy, the battery does work on the electrons to put them back in the negative terminal so they are full of energy and reenter the circuit.

This explanation is very great because it answers questions : why does putting 2 batteries in series double the voltage? (because work has to be done two times on the electrons in the battery, so the potential energy doubles). Why connecting - of battery 1 to + of battery 2 without connecting + of battery 1 to - of battery 2 doesn't create electricity (because the electrons have to do a complete loop in the circuit and return to their starting point to make electricity for a long time. There is no external wire connecting - of battery 2 to + of battery 1 so there isn't a complete loop).

However, from what I understand of batteries, there is no electron that moves from the positive terminal to the negative terminal of the battery. The electrons of the circuit all come from the negative terminal and once they reach positive terminal there is nothing else happening except making the electrolyte ions neutral. They don't return to their starting point.

So could someone prove to me that inside a battery, electrons from the positive terminal are done work on and go to the negative terminal.

Or if this theory is false, could someone answer the two questions above that are easily answered by this theory in another way?

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  • $\begingroup$ Actually, individual electrons often do not complete a loop. The electron drift velocity is about 100 micrometers/second in copper, see resources.schoolscience.co.uk/CDA/16plus/copelech2pg3.html . The charge motion is more like the "Newton's cradle" demo, where each electron's EMF field pushes the next electron. $\endgroup$ – DrMoishe Pippik Dec 23 '16 at 20:28
  • $\begingroup$ I know that electrons have a pretty slow drift velocity, but do the electrons that end up in the positive terminal of a battery return to the negative terminal? From all that I understand the answer is no, they detach themselves from the positive terminal to go in the electrolyte making some positive ions neutral but that's it. $\endgroup$ – gigi Dec 23 '16 at 21:20
  • $\begingroup$ The electrons in a battery never complete a full circuit back to the starting point. In a DC generator, they would, as the magnetic field impels them indefinitely. In a battery, as @TAR86 states, the chemicals are consumed. $\endgroup$ – DrMoishe Pippik Dec 24 '16 at 23:29
  • $\begingroup$ Then what about the two last paragraphs of this text : physicsclassroom.com/class/circuits/Lesson-1/Electric-Potential ? $\endgroup$ – gigi Dec 25 '16 at 2:17
  • $\begingroup$ "Positive test charge" is not "electron". $\endgroup$ – DrMoishe Pippik Dec 25 '16 at 2:45
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There are many ways of approaching the subject as has been illustrated by the answers so far. There is nothing wrong with them, except that they do not answer your question - I think.

Kirchoff says that current must flow in a complete loop. If the charge did not get back to the very starting point, there would be an accumulation of charge somewhere. This would cause the voltage at that spot to increase, which would then motivate charge to move faster from that location. So, your question, as I see it, is one of taking Kirchoff on face value and asking where and how the flow path is completed?

All batteries have a solid part and a liquid part. The liquid part separates the two electrodes and is where the circuit is completed. When an electron leaves one pole and goes through the external circuit one NEGATIVELY charge ion comes out of solution and attaches to that pole. Similarly, when a negative electron arrives at the other pole through the external circuit, a negatively charged ion enters the solution. The solution then completes the circuit, as in, one negative charge has left solution and one has been gained, leaving no net charge on any pole (except for the net that is there creating the voltage. The exact chemistry depends on the reactants involved.

This argument is simplified and very general. Positive ions also take part going in and out of solution, but in the opposite direction.

But leaving the simple model described in place, we can ask the question: Why do the ions in solution behave the way they do? The answer is that they are motivated to do so AGAINST the voltage that exists because they "want" to chemically react at the poles. It is the chemical energy expended that moves them against the voltage and causes them to move in that manner.

I hope this helps.

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For a moment I would suggest you to forget about electrons,their flow ,batteries and stuff. Assuming that you have the basic intuitions regarding the principles of Newtonian mechanics and work done and all I would like to proceed in a different way. Suppose you are standing now on a ground and you have a ball in front of you lying on the ground. It doesn't lift itself up in the air, which is a common observation we all have made by now. But when you wish to lift it up to some height,be it h, then you expend your ATPs and chemical energies in your muscle to lift the ball slowly to that height h , and in doing so you did a work exactly equalling mgh ( neglecting air drag) . Now you take a tube of some arbitrary shape ( just to give a proper intuition) such that the ball is at its one end and the other end meets the ground. Then you leave the ball and it cleverly curves through the tube and gets back to ground level. This is exactly what we find in a battery system. It pumps electrons, against an opposing conservative field and then allows them to fall back. Here ,there's no man power but the chemicals do the trick by getting indulged into some redox reactions. Now ,if you think of those questions from this perspective hope you will be able to answer them efficiently.

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I believe that it is possible to extend your theory a little bit and make it work for batteries. The crux lies in your sentence (emphasis mine):

When the electrons arrive in the positive terminal and they lost all of their potential energy, the battery does work on the electrons to put them back in the negative terminal so they are full of energy and reenter the circuit.

Remember that a battery has a finite capacity (at some point, its voltage drops to 0 because it was in use long enough or it corroded). Thus, you can think of your "negative terminal" as a reservoir for electrons on which the manufacturer of the battery has done work. Once that reservoir is empty, voltage drops. It is not necessary for the electrons to "completely" make a full loop, they merely need to move from one terminal to the other, but do not need to return. (I note here that some commenters correctly remarked that given the drift speed of electrons, one cannot very well say that a single electron travels the entire circuit. It seems more reasonable that it is like an open pearl necklace: push a pearl onto one end, on the other end a pearl will leave the string. But electrons are indistinguishable from each other anyway)

In this regard (as long as one deals with DC, not AC), a single battery can be thought of as a single charged capacitor, except that instead of an electrical potential difference, you have an electrochemical/chemical potential difference.

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