Re: EMF +- battery speculation

["John S. Denker" <jsd@MONMOUTH.COM>]

Shawn Knudsen wrote:
> > I think you should stick with "electromotive force" yet explain the
> > appropriate concept to your students.  The reason I say this is simply
> > that after your students leave your classroom, the rest of the world
> > (barring a few on this Phys-L list) will refer to EMF as "electromotive force."

Ludwik Kowalski wrote:
> You are probably correct

What is the evidence of that?  So far NO EVIDENCE has
been adduced.

If your students take a battery into a Radio Shack store
and ask somebody to help them measure the EMF, they will
be considered weirdos, if they are understood at all.

It would be like going into Home Depot and asking to buy
a doornail.

If you doubt my assertion, go to Radio Shac and do the
experiment.  While you're there, count the number of
objects that are labelled as to EMF. Compare that with
the number of objects labelled as to voltage.

I recommend you do not waste time teaching students about
doornails.  I recommend you do not waste time teaching
about EMF.  In modern usage
 -- EMF stands for ElectroMagnetic Fields (a health issue)
 -- EMF is the name of a rock band
 -- EMF is the name of a firearms manufacturer
 -- EMF stands for Electronic Music Foundation

The notion of electrodynamic "force" essentially does
not exist outside of a few out-of-date schoolbooks.

If there is a concept here at all, it is the concept of
Thévenin-equivalent open-circuit voltage.  I recommend
you teach that concept and that terminology.

[in a battery]
> 1) There is no load to begin with. Is it true that most of the
> electric flux is in the acid between the plates,
> as in a charged capacitor? I think so.

I don't think so.  There is no field and no flux in the
electrolyte of an unloaded battery.

> But the electric field between the plates
> does not produce a current inside the electrolyte. Free carriers
> are available but they do not drift. Why not?

Because there is no such electric field.
If there were an electric field, the charges would drift.

> Because in addition
> to the electric force (Fe=q*E) each carrier experiences another
> force, equal and opposite to Fe. This non-electric force was
> labeled as emf.

This is a fairy tale.  Further speculation along this
line is not going to be helpful.