I am taking the Coursera course on DC linear circuits and have various questions in parallel. I found the 80% related question "How does current flow through a voltage source" and my question differs in that it is related to a capacitor-battery circuit as described by the Organic Chemistry Tutor here. According to Organic Chemistry Tutor, in a circuit with a "+" battery pole connected to one capacitor's plate and a "-" pole - to another, the battery pulls electrons from one capacitor's plate and makes them flow through the "+" pole, the battery itself and it's "-" pole to another plate thus charging the capacitor. The question is why aren't electrons from the plate attracted to the "+" pole of the battery by sticking to the cathode (reduce it by giving up the electrons) ? A parallel question is why the electrons from the plate aren't repelled back by the "-" pole of the battery and rather flow through it?

As is mentioned in the related question, the electrolite in the battery actually conducts the electrons pulled from the capacitor's plate. A subquestion may be: should the current in such circuit consist from both electrons pulled from the capacitor's plate and the electrons supplied by the battery?


4 Answers 4


All capacitors and batteries use dielectrics which are all insulators and (ideally) will not conduct on their own internally.

Dielectrics are polar but do not release electrons like metals , which is why they insulate electrically.

capacitors do not store charges

It is actually a misnomer to say dielectrics store any charges. The charges always exist regardless of the voltage , but they become polarized with an externally applied voltage or current with an electric field which polarizes the molecules to align in orientation and closer to the plates by opposite polarity attraction and similar polarity repulsion.

Once any external current stops or the circuit is disconnected and the dielectric has a voltage collected by the plates, the insulators retain the net charge from an imbalance charge closest to each electrode as the orientation of spin of each each atom accumulates to create this net charge imbalance.

Just as the ferromagnetic materials create a magnetic field by rotating atom’s polar alignment, so do dielectric insulators by aligning the electron spin angle and attracted in the direction of the opposite plate polarity.

By convention we use current flow in the opposite direction of physics for a more logical understanding and convenience to avoid confusions.

Here the EMF electron force field is shown with current flowing thru the plates.


What flows are displacement currents, changes in electric field density with time which cause effects similar to currents.

  • \$\begingroup\$ This implies that "Current doesn't actually flow through batteries", ok. \$\endgroup\$ Jun 27, 2021 at 15:22

Electrons from the positive plate are attracted to the positive terminal of the battery, and repelled from the negative terminal, that’s what causes current to flow. Inside the battery, electrons are actively pumped towards the negative terminal. And yes, the current in the circuit does consist of electrons being both drawn into and pushed out of the battery, although in this case these take place in different parts of the circuit, but must be equal unless the net charge of the battery is to change (which it usually doesn’t, although it could form one plate of a capacitor under contrived circumstances).

  • \$\begingroup\$ While electrons from the plate are attracted to the + terminal of the battery which they encounter before the negative, why won't they stick to the + ions in the + terminal by filling their valence electron shells and thus neutralizing the positive terminal itself? \$\endgroup\$ Jun 27, 2021 at 0:30
  • \$\begingroup\$ @amts that will happen initially but the battery is constantly trying to push electrons from the positive to the negative terminal, and so it will keep doing so until the charge on the plates equals the battery voltage, at which point the forces in the electrons are in balance and current stops flowing. Or are you asking how batteries work? I used to tell my daughter about such things to get her off to sleep at night. \$\endgroup\$
    – Frog
    Jun 27, 2021 at 3:23
  • \$\begingroup\$ Assuming an external current flow through a battery (which is likely in a circuit with several resistive loads and several batteries, as I saw in mesh analysis problems), it is unclear how the battery's electrolyte can serve a dual conductive function for both battery's internal charges and an external circuit's electron current without interference between them (i.e. the 2 types of charge movements - battery's internal and circuit's external). \$\endgroup\$ Jun 27, 2021 at 15:18

Current doesn't actually flow through batteries

The atoms on either side of the battery undergo chemical reaction that cause them to release or accept electrons.

Once all the chemicals done their trick the battery is depeleted and current stops flowing.

current flows in one end an out the other but in the middle it's chemicals doing chemical things, not electron current.

It's like all the electrons that come out of the negative terminal were put there in the factory. Each zinc atom provides 2 electrons, Once all the zinc atoms are dissolved into \$Zn^{++}\$ ions it's game over.

Similarly on the other electrode \$MnO_2\$ is converted to \$Mn_2O_3\$ while converting water to hydroxide ions (which combine with the zinc ions produced at the other electrode)

As for why the charge of the capacitor doesn't stop the battery from producing current.

Actually it does. when the voltage on the capacitor matches what the battery is capable of the current stops flowing.


How Batteries Work


This video shows that chemical reactions, known as oxidation reactions and reduction reactions, force negative ions to accumulate at the negative terminal of the battery. A separator prevents these ions from flowing inside to the battery to reach the positive terminal. When connected to the battery using conductive wires the battery potential Vbat appears across the capacitor plates. However if the initial voltage across the capacitor is Vc = 0 then the potential across the capacitor rises over time as follows. Electrons flow onto the negatively charged capacitor plate, this induces a force on the electrons in the positively charged plate, driving electrons away from the surface of the positively charged plate. The potential across the capacitor rises from Vc = 0 to Vbat which stops the flow of current at the steady state equilibrium.

This 28 page reference:


On nominal page 4 shows conduction mechanism at the surface of electrode for a lead acid battery. "A charged sulfate ion approaches uncharged lead atom on surface of electrode. Lead atom becomes ionized and forms ionic bond with sulfate ion. Two electrons are released into lead electrode." Page 6 shows conduction mechanism at the surface of the positive electrode.

Electrons that arrive at the positive terminal of the battery recombine with chemicals internally but this does not block a flow of current external to the battery. The capacitor eventually blocks further flow of current when the system reaches the steady state equilibrium.

  • \$\begingroup\$ I've watched and screenshoted this tutorial before I've got the question posted. As is mentioned in the related question referenced above, current external to the battery (as in a capacitor charging circuit) flows through battery's electrolyte which is actively used by the redox reactions to produce battery's voltage. How can an external current flow through the same electrolyte and not interfere with the redox reactions? \$\endgroup\$ Jun 27, 2021 at 17:04
  • \$\begingroup\$ Oxidation-reduction reactions or redox reactions transfer electrons from one chemical element to another. The external current in a copper wire is due to electrons (free charge carriers) in the conduction band of copper. The internal current in the capacitor is called a displacement current. Think of the chemicals in the battery as a bucket brigade for electrons, negatively charged ions, and/or positively charged ions. The chemicals force negative charge carriers toward the negative electrode. The electrons or ions do not interfere with reactions they are part of the chemical reactions. \$\endgroup\$ Jun 27, 2021 at 23:13

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