Something that bothered me was that the anode and cathode in a battery cell
seem to be shorted out (if you consider the electrolyte a conductor). I read
about this and now I'm thinking the *only* reason they are not shorted out
is this: ionic conduction is different than conduction through metal (in
this case the current in the metal flows opposite the current carried by
ions). The metal cannot conduct ions and the electrolyte cannot conduct
electrons. Does this sound correct?

Rick

Rick Giuly ), in article , wrote:
Something that bothered me was that the anode and cathode in a battery cell
seem to be shorted out (if you consider the electrolyte a conductor). I read
about this and now I'm thinking the *only* reason they are not shorted out
is this: ionic conduction is different than conduction through metal (in
this case the current in the metal flows opposite the current carried by
ions). The metal cannot conduct ions and the electrolyte cannot conduct
electrons. Does this sound correct?

It sounds pretty close to me, except to note that ions are merely
charged particles. You could replace the word "ion" with "anion" to make
it more descriptive. A stickler for accuracy would say that "cannot" in
your last sentence is too absolute. "doesn't" or "generally doesn't" would
be better terms in that context.

"Rick Giuly" wrote in message ...
Something that bothered me was that the anode and cathode in a battery cell
seem to be shorted out (if you consider the electrolyte a conductor).

But where does the battery voltage-drop come from? Does is
arise out in the electrolyte, or inside the metal? Nope.
It appears at a molecule-thin layer called the "Helmholtz
double layer" where electrolyte touches metal.

Essentially, the battery *is* this molecule-thin layer. You
can remove most of the metal in the plates, and you can make
the electrolyte layer very thin, yet the battery is unchanged.
All the important stuff is happening in that tiny layer.

The metal is certainly a conductor, and so is the electrolyte.
But what about the thin layer between the two? If that layer
causes the battery's voltage, would that layer also be a conductor
which shorts out the voltage at the same time? Simple answer:
the layer is a charge-pump which puts out "constant pressure"
or potential. The pump runs just enough to create a particular
voltage drop, then it stops.

Analogous question: when running, is a water pump a short circuit
or an open circuit? A water pump creates a pressure-difference,
so why doesn't the water circuit short itself out through the
pump (i.e. why doesn't the water just instantly flow backwards
through the pump and wipe out any pressure difference the pump tries
to create?) Answer that, and you'll have an idea of how the
charge-pump at the surface of the battery plates operates.

PS, there are TWO charge pumps in any battery, one on each
plate, and they fight each other. If the two metals in the
plates are identical, then the charge-pumps fight to a standstill
and the output voltage difference is zero.

(William J. Beaty) wrote in message . com...
"Rick Giuly" wrote in message ...

Something that bothered me was that the anode and cathode in a battery cell
seem to be shorted out (if you consider the electrolyte a conductor).

But where does the battery voltage-drop come from? Does is
arise out in the electrolyte, or inside the metal? Nope.
It appears at a molecule-thin layer called the "Helmholtz
double layer" where electrolyte touches metal.

Essentially, the battery *is* this molecule-thin layer. You
can remove most of the metal in the plates, and you can make
the electrolyte layer very thin, yet the battery is unchanged.
All the important stuff is happening in that tiny layer.

The metal is certainly a conductor, and so is the electrolyte.
But what about the thin layer between the two? If that layer
causes the battery's voltage, would that layer also be a conductor
which shorts out the voltage at the same time? Simple answer:
the layer is a charge-pump which puts out "constant pressure"
or potential. The pump runs just enough to create a particular
voltage drop, then it stops.

Analogous question: when running, is a water pump a short circuit
or an open circuit? A water pump creates a pressure-difference,
so why doesn't the water circuit short itself out through the
pump (i.e. why doesn't the water just instantly flow backwards
through the pump and wipe out any pressure difference the pump tries
to create?) Answer that, and you'll have an idea of how the
charge-pump at the surface of the battery plates operates.

PS, there are TWO charge pumps in any battery, one on each
plate, and they fight each other. If the two metals in the
plates are identical, then the charge-pumps fight to a standstill
and the output voltage difference is zero.

Bill, you alone would be enough to keep peeking in sci.physics.

Did you happen to see my battery/EMF question?

One might wonder, allied to this question, is that if the charge
carriers in a battery are subject substantially only to one force, the
EM field, just what is it that pumps them uphill wrt to the EM field?

Why, the EM field, of course.

Actually, it was a naive Platonic question, so not too many people
bit. Essentially charge carriers in conductors -- including resistive
conductors and EMF producing conductors -- even very thin Helmholtz
double layer conductors, are only subject to one force. And on
average, their velocity is constant (that is, their average or drift
velocity is constant), so therefore, the time averaged microscopic
field acting on them is zero.

So I argue.

So what's going on? I would further argue that a battery is
essentially the flip of a resistive wire, and what's really going on
in either case is a war of macroscopic average EM fields and detailed
microscopic EM fields -- I should probably just say "electric" -- on
the battleground of entropy.

Or something like that.

On average the electric seen by the particle is zero (i.e., on time
average, at least), and that is no contradiction. It just means, in
its average wanderings, the charge carrier is serving as the pawn of
entropy -- in the case of the battery, being pummeled up the spatial
average field slope by the slings and arrows of outrageous microscopic
collisions, in the case of the wire, being impeded in its progress
down the charge slope (obviously in a battery both are going on, but
keep it simple).

I'm not 100% sure about the per particle time average (=0) as distinct
from a per distance ...

Aha!

I think the correct statistical distinction is really path/point.
That would be a typical kind of statistical "paradox". The path
average -- hence also time average -- of individual carriers is zero
(mean velocity invariant), whereas the time or spatial average
_uncorrelated with the presence of a particle_ is non-zero, and in
fact equal to the "macroscopic electric field".

You have to have seen a few statistical paradoxes to have a feel for
them.

Anyway, not many people bit my question, and the predominant "serious"
answer seemed to be "study QED" -- which is nonsense, IMHO. If the
answer to a question which has a perfectly comprehensible answer
within some classical approximation is "study the QM version", this
shows a lack of understanding of the system. If one can't answer a
classically answerable question in classical terms, then when one gets
to QM, one has about zero chance of understanding what's going on --
even if by some miracle we manage to grind through a derivation
producing an expected result. The result will be a feeling that the
explanation is buried in the magic of QM, hidden from mortal eyes.