General > General Technical Chat

Does current flow through a Battery?

<< < (6/11) > >>

ejeffrey:

--- Quote from: GlennSprigg on October 22, 2021, 01:31:45 pm ---So far, no-one here has dared/tried to counteract what I said about a 'Capacitor',

--- End quote ---

Because the title of the thread is "does current flow through a battery".  Responding to a description of what is happening with ionic flow inside a battery with "but a battery is basically like a capacitor" is called moving the goalposts and is actually rather rude.  It's fine to ask about capacitors as well, but to use that to derail an explanation and then try to go back and claim that your "what about a capacitor" question is evidence that the answer for batteries is wrong is not really OK.


--- Quote ---(which IS basically behaving like a battery,

--- End quote ---

In that it stores and releases electrical energy, yes.  Otherwise, not so much.  If you have a problem with the explanations of charge movement in batteries go ahead and ask, but if you don't, just move on.

Anyway, given that batteries have already been explained in detail:


--- Quote --- where there is NO actual flow of 'charge' within it, through the Dielectric

--- End quote ---

So I don't care to debate whether displacement current is "real" current, but even setting that aside this is technically wrong in most cases.

In a vacuum gap capacitor you are correct that there is no charge flow in the gap.  But very few real capacitors are made this way.  Generally they have a dielectric that has relative permittivity >> 1. A dielectric is just a bunch of positively charged nuclei and bunch of electrons bound to them.  Unlike in a metal, the electrons cannot flow over long distances but when an electric field is applied (by charging up the capacitor), each electron moves slightly towards the positive electrode while staying bound to the same area.  That is a moving charge and thus a current.  How big is that current?  The material polarizability is exactly a measure of this charge movement.  If you have a capacitor dielectric with relative permittivity 10 and 1 amp RMS is flowing in/out of the capacitor from the external circuit then there is 900 mA of dielectric charge motion and 100 mA of vacuum displacement current.  Even if you say the vacuum displacement current doesn't count the other 90% is physical charge movement.

We don't normally worry about this.  Dielectric polarizability has exactly the same mathematical form as the vacuum permeability.  For Maxwell's equations in matter J only refers to "free" current, and the motion of bound charges within a dielectric is just combined with the displacement current into a single term.  But if you want to be pedantic, you should at least do so correctly :)

GlennSprigg:

--- Quote from: TimFox on October 22, 2021, 02:36:47 pm ---"Displacement current" was discovered in the 19th Century and is included in Maxwell's Equations to explain the current through a capacitor.
Ionic current in batteries is similar to ionic current in salt-water solutions.
Current is a more general term than the motion of electrons in a vacuum tube.

--- End quote ---

Sorry Tim....  I love you as a tech contributor here, (I highlighted in BOLD your last sentence of concern)...
Again, it seems to be  about 'nomenclature' and  not about present acceptance of 'standards' ??
I 'guess' I'm taking it to my grave then... but I can NOT accept that there is 'any' CURRENT flow that is 'not' involving
actual 'Electrons', as we  understand today...  and I will never think any other way!   :palm:

TimFox:
Electricity and thermodynamics were first treated like hydraulics, involving flow of some kind of fluid, before elementary particles were discovered.
Early on, the important difference about electricity was discovered, that it involved opposite charges that could be called positive and negative.
Only later were the particles discovered, but current of all kinds and charge carriers (including protons) remained, roughly following the original rules.
"Displacement current" was added to the inventory of current types in order that current around a circuit, however formed, followed the continuity rules.
The point that I persist in making is that electric current is more general than electron flow, although electron motion is certainly a form of current.

bdunham7:

--- Quote from: GlennSprigg on October 24, 2021, 12:14:48 pm ---I 'guess' I'm taking it to my grave then... but I can NOT accept that there is 'any' CURRENT flow that is 'not' involving
actual 'Electrons', as we  understand today...  and I will never think any other way!   :palm:

--- End quote ---

What would you call a beam of protons or alpha particles?

SilverSolder:

--- Quote from: GlennSprigg on October 24, 2021, 12:14:48 pm ---
--- Quote from: TimFox on October 22, 2021, 02:36:47 pm ---"Displacement current" was discovered in the 19th Century and is included in Maxwell's Equations to explain the current through a capacitor.
Ionic current in batteries is similar to ionic current in salt-water solutions.
Current is a more general term than the motion of electrons in a vacuum tube.

--- End quote ---

Sorry Tim....  I love you as a tech contributor here, (I highlighted in BOLD your last sentence of concern)...
Again, it seems to be  about 'nomenclature' and  not about present acceptance of 'standards' ??
I 'guess' I'm taking it to my grave then... but I can NOT accept that there is 'any' CURRENT flow that is 'not' involving
actual 'Electrons', as we  understand today...  and I will never think any other way!   :palm:

--- End quote ---


Here's an interesting mind-bending thought experiment for you:

1.  Grab an air capacitor with two plates.
2.  Put a flat copper coil between the two plates (e.g. one to 10 turns).  Place it flat like the plates, right in the middle of the gap, but not touching the capacitor plates.
3.  Apply a moderate frequency AC voltage to the air capacitor, say 1KHz, so we don't have to deal with RF radiation

Q:  Will the coil pick up a signal (indicating that a current is flowing through the middle of it)?

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod