Do electrons flow through a battery or is it something else?

Delta2 · May 26, 2022

I still remember a phrase from my physics textbook in the secondary high school (ages 15-18, we call it Lykeio here in Greece), (direct translation from Greek follows):
"An EMF source doesn't supply a circuit with electric charge but it sets in motion the electric charge already present in the circuit"

Tbh I am not sure if this phrase is 100% correct but I am just mentioning it...

vcsharp2003 · May 26, 2022

jbriggs444 said:

It is not clear what you are asking. What do you mean by "contribute to"?

I mean, obviously it is the motion of charges (electrons) in the conductor which defines the electric current in that conductor. But I do not know whether that fits what you mean by "contributes to".

By contribute I meant move in the conducting wire of external circuit. Do the battery electrons on its -ve electrode/terminal also move as a current I in the external circuit or its the conductor electrons only that move as a current I ? I got the answer as mentioned in UPDATE 1 of my post. Both i.e conductor electrons as well as battery electrons will move through the conductor wire when current I flows through it

vcsharp2003 · May 26, 2022

Delta2 said:

An EMF source doesn't supply a circuit with electric charge but it sets in motion the electric charge already present in the circuit

I see a catch in above statement. Once all free electrons in conductor have flown to the +ve electrode of battery in the external circuit, then there will no more free electrons left in the conducting wire and so the current would stop due to lack of free electrons . Right? So, the battery must supply electrons to maintain the flow i.e to maintain the current.

hutchphd · May 26, 2022

There is no way to tell. Electrons are indistinguishable by the tenets of Quantum Mechanics. Somehow batteries use stored energy to internally segregate charge to maintain a fixed electrical potential across their electrodes. That's what they do: the details usually involve selective motions of various charged items: the details are interesting but not directly salient. When an external conductor is attached to the battery electrodes, charges move to mimize this potential energy. Usually the conductor is a metal and the charges that are mobile are the "conduction" electrons. The energy is in fact carried by the associated fields. The rest is detail.

/

jbriggs444 · May 26, 2022

vcsharp2003 said:

I see a catch in above statement. Once all free electrons in conductor have flown to the +ve electrode of battery in the external circuit, then there will no more free electrons left in the conducting wire and so the current would stop due to lack of free electrons . Right? So, the battery must supply electrons to maintain the flow i.e to maintain the current.

Have you looked at the electron drift velocity for a wire, divided the wire length by the drift velocity and compared the result to the discharge lifetime of the battery at the current in question?

Wikipedia has a numerical example for drift velocity.

vcsharp2003 · May 26, 2022

jbriggs444 said:

Have you looked at the electron drift velocity for a wire, divided the wire length by the drift velocity and compared the result to the discharge lifetime of the battery at the current in question?

Wikipedia has a numerical example for drift velocity.

Drift velocity is of the order ##10^{-5} m/s##, so it's extremely small. So, what you're saying is that the speed of electrons flow is too less for all the conductor electrons to reach the +ve terminal of battery. Right? It's like the electrons drift i.e. move forward in current direction at an extremely slow pace.

nasu · May 26, 2022

At the cathode of a cell some positive ion from the solution (electrolite) gets neutralized by "capturing" electrons. These electrons are from the metallic cathode which is part of the circuit. I suppose these electrons are from the conduction band of the cathode even though I did not find this explicitly stated. On the other hand, at the anode metallic atoms go into solution as positive ions and they "leave behind" some electrons in the process. So overall, the number of conduction electrons in the external circuit remains the same. It is not a change in the nuber of electrons that drives the current but the potential differences created at each interface electrode-solution. Oberall, the battery does not provide any charge to the external circuit and it does not store charge, of course.

jbriggs444 · May 26, 2022

vcsharp2003 said:

Drift velocity is of the order ##10^{-5} m/s##, so it's extremely small. So, what you're saying is that the speed of electrons flow is too less for all the conductor electrons to reach the +ve terminal of battery. Right? It's like the electrons drift i.e. move forward in current direction at an extremely slow pace.

Yes, that is the idea.

They move in the opposite direction of the "conventional current". If the wire is short and the battery has a large capacity (high amp-hours), electrons may be able to make the trip. If the wire is long and the battery has a low capacity (low amp-hours), electrons may not be able to make the trip before the battery is drained.

None of which matters. Electrons are, as far as we know, indistinguishable. Which ones are passing a particular point is irrelevant.

vcsharp2003 · May 26, 2022

jbriggs444 said:

Yes, that is the idea.

They move in the opposite direction of the "conventional current". If the wire is short and the battery has a large capacity (high amp-hours), electrons may be able to make the trip. If the wire is long and the battery has a low capacity (low amp-hours), electrons may not be able to make the trip before the battery is drained.

None of which matters. Electrons are, as far as we know, indistinguishable. Which ones are passing a particular point is irrelevant.

The speed due to drift velocity seems to be less than even snail pace. ##10^{-5} m/s ## is equivalent to ##0.000022 mph## or ## 0.000036 km/h##.
And if we assume a conducting wire of 0.5 m length connecting the battery terminals, then it would take an electron to complete the full circuit about 13.89 hours which is a very long time.

I used to think that electrons are traveling very fast in a wire when a current flows.

Tom.G · May 26, 2022

And what electrons lack in speed they make up for in quantity.

One Ampere is defined as 6.28 ×10¹⁸ electrons per second.
(6 280 000 000 000 000 000 per second)

vcsharp2003 · May 26, 2022

Tom.G said:

And what electrons lack in speed they make up for in quantity.

One Ampere is defined as 6.28 ×10¹⁸ electrons per second.
(6 280 000 000 000 000 000 per second)

Very interesting facts about electric current. Even 1 billion electrons per second is too small for above quoted number.

jbriggs444 · May 27, 2022

vcsharp2003 said:

if we assume a conducting wire of 0.5 m length connecting the battery terminals, then it would take an electron to complete the full circuit about 13.89 hours which is a very long time.

A 12 volt automotive battery can deliver about 48 amp-hours of charge. So one of those could drive its electrons all the way through that 0.5 meter wire before running out of charge.

The electrons still would not complete a full circuit, however. Each one of the six series-connected cells in a car battery has the ability to absorb the entire 48 amp-hours of charge.

Tom.G · May 28, 2022

jbriggs444 said:

The electrons still would not complete a full circuit, however. Each one of the six series-connected cells in a car battery has the ability to absorb the entire 48 amp-hours of charge.

Then where would they congregate?

hutchphd · May 28, 2022

I think we do no service by re-enforcing a picture of electrons, each apparently having a name (but no possible nametag) marching single file through the circuit. I understand it is the simplified picture we likely all learned in primary school, but it leads to ill-conceived notions. The fields carry the energy and the wires guide the fields. There is no FILO (first in last out) requirement for them.
As to the OP: