Re: Voltaic Pile of Confusion

[William Beaty <billb@ESKIMO.COM>]

On Sun, 30 Jul 2000, Tom McCarthy wrote:

> When I refer to the "produced" electron, I meant the free charge that is
> created (there I go again!) in the chemical reaction.

No free charge is created on average.  The metal plates are always filled
with free charges, and the battery's electrolyte is always filled with
free charges.  As a battery creates an electric current, the total number
of free charges does not change.  In a coil/magnet generator, do we say
that free charge is created?  Nope, and the same applies to batteries.
Batteries and generators TRANSPORT charge but do not create any.  We
should not concentrate on the negatvie terminal where electrons are being
expelled, because there are electrons already at the positive terminal,
and they are being sucked into the battery.

There are two chemical reactions involved, and each reaction drives
charges BETWEEN the electrolyte and the metal, creating an electric
current with a path that's directed through the battery.

The reaction at the negative plate is taking neutral atoms and wrenching
them apart into electrons and positive ions which then flow in opposite
directions.

Here's the tricky part: by driving opposite charges in opposite
directions, the chemical reaction is creating a net current ACROSS the
metal/electrolyte interface.  Weird, or what?!!!  This is a key concept
needed to understand what batteries are all about.

    __________
   |          |
   |          |
   | (-) ---> |  <---  (+)
   |          |
   |          |
   |          |
   |  METAL   |  ELECTROLYTE
   |__________|


  THE IMPORTANT PART:   In the above diagram, the direction of the
                        electric current is RIGHT TO LEFT.
                        The opposite charges flow together and
                        cancel out, but the path of the current
                        is different: it goes right to left



And at the positive plate, the chemical reaction is pushing positive ions
from the electrolyte together with electrons from the metal, which creates
neutral atoms.  Again, this reaction is pumping charges ACROSS the
metal/electrolyte interface.

By PULLING opposite charges apart, a driving force is created which acts
as a charge-pump.  The same applies to situations where opposite charges
are PUSHED together.


>  Clearly, the chemical
> constituents are neutral to begin with and that there is a monstrously large
> positive charge awaiting the electrons return.

This sounds like the "empty pipes" misconception.  Metals are not like
hollow pipes.  They are full of free electrons.  If you imagine that wires
are like pipes, then imagine them as being pre-filled with "electric
fluid." An electric current is not a fast flow of a few electrons in a
hollow wire.  Instead it is a slow flow of vast numbers of electrons in an
electron-filled wire.  The electrons are not produced by the battery, they
are "produced" by the wires. Some books say that electrons in an electric
current are flowing at the speed of light.  They are wrong.


>  The chemical reaction that
> produced this situation, created a potential difference (i.e.., the products
> of the reaction are at a lower potential than the reactants).  If each
> battery gives its free electron a certain voltage, then, if this electron
> enters another battery, it is given another kick as it participates in the
> next batteries chemical reaction, and so on.  My question then is why does a
> voltmeter measure the extreme voltage, as though all the electrons traveled
> through all three batteries, as opposed to an average?

I think you will get into trouble if you think in terms of individual
electrons.  That's like trying to describe pressure, but then thinking in
terms of the "pressure" of a single water molecule.  It doesn't work!  A
large population of water molecules can have a pressure, but individual
molecules do not.


Here's the specific problem:  say we have two separate metal wires laying
on the table.  If I take some electrons out of the electron-sea of one
wire and place them onto the other wire, a voltage appears across the
wires.  The WIRES have a voltage between them, but the individual
electrons do not "have" voltage.

In a string of batteries in series, why do the voltages sum together?
Simple:  because whenever you connect an object to a positive battery
terminal, that object becomes electrically charged.  If our "object" is
another battery, then the WHOLE BATTERY becomes positively charged... and
also the positive plate of the added battery is charged to twice the level
of the single battery.

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