0
$\begingroup$

How can current flow continue and pass through the battery, if the electric field inside battery is in the opposite direction than the one inside the wire.

Let us assume positive charges and conventional current flow. Inside the battery, the E field points the other way, assuming battery +____- the E field points this way $E_s$---->, meanwhile current flows <---- . Conversely, the E field in the wire <-----$E_w$.

How the current flow continues and passes the battery if there are 2 E field opposing each other? ($E_s$ denotes the efield at the source and $E_w$ the Evfield at the wire due to the potential difference created by the source). In fact, I would think that $E_s$ is stronger than $E_w$, but that would imply an opposite current flow again, but this again goes against the initial idea that we are talking about positive charges flow.

$\endgroup$
1
  • $\begingroup$ Batteries are powered by chemical reactions, which release chemical energy to move the electrons against the e-field $\endgroup$ Mar 26, 2021 at 12:12

1 Answer 1

0
$\begingroup$

Current flows in the opposite direction of the E field in a battery because a chemical reaction at the electrode surface does work on the charges and physically pushes them against the electric field.

It is important to recognize that the charge carriers in an electrolyte are ions, not electrons. The ions cannot move in the electrode so they are stopped at the electrolyte surface. The electrons cannot move in the electrolyte so they are stopped at the electrode surface. Thus at the interface between the electrode and the electrolyte current flow can only happen through a chemical reaction that produces or consumes an electron in the electrode and produces or consumes an ion in the electrolyte.

When this chemical reaction is energetically favorable then the reaction will proceed against the E field. This does work on the charges converting energy from chemical to electrical. Of course, the larger the opposing E field the slower the reaction, and at a characteristic voltage the reaction stops. This is the battery’s open circuit voltage. Conversely, even if there is no opposing field, the reaction can only proceed at a certain rate. This is the battery’s short circuit current. Between those limits the battery will push current against an E field.

$\endgroup$
5
  • $\begingroup$ If we forget the term battery and view this from a vector field point of view. Let's remove the term battery and how it works. We have one electric field pointing on the left, $E_w$ generated due to the potential difference across the wire and the field of the source $E_s$ pointing the other way around. Let's call it a source and forget it is a battery. Assuming that the positive charges are reaching the negative end, the $E_s$ should push them in the opposite direction than the one they arrive. Only if $E_w$ is greater than $E_s$ (the way I think it) this flow can continue. Am I wrong? $\endgroup$
    – bigboss
    Mar 26, 2021 at 13:16
  • $\begingroup$ @bigboss there is only one E field. Decomposing fields is tricky, and it is easy to make $E=E_s+E_w$ such that both $E_s$ and $E_w$ violate Maxwell’s equations. I would not recommend haphazard field decompositions. Instead, think of a battery as having something like the opposite of Ohm’s law. Instead of having current in the direction of the E field and consuming electrical power it has current in the opposite direction and provides electrical power. $\endgroup$
    – Dale
    Mar 26, 2021 at 14:33
  • $\begingroup$ Yea but still the efield we show on the source contradicts the one that generates the current flow inside the wire... this breaks my intuition of the forces that make the charges move around. $\endgroup$
    – bigboss
    Mar 26, 2021 at 15:11
  • $\begingroup$ @bigboss you are thinking that a battery follows Ohm’s law. It doesn’t. In a battery the current goes in the opposite direction from Ohm’s law. The battery provides a chemical force that physically pushes the charges in the opposite direction of the electrical force. Sometimes that chemical force is called an EMF. It is this chemical force which drives the current, despite the E field opposing it. It is just like if you put charges on the end of a stick and then push the charges using the stick. Not all materials follow Ohm’s law $\endgroup$
    – Dale
    Mar 26, 2021 at 16:12
  • $\begingroup$ Ok but the current inside the battery we assume is less than the one flowing inside the wire right? Else either the net current would be zero if it was equal or the flow would be opposite. $\endgroup$
    – bigboss
    Mar 26, 2021 at 18:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.