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Re: EMF



Bob Sciamanda wrote:

How about the PD produced by diffusion across a
semiconductor NP junction?

He was responding to John S. Denker who wrote:

crawford j maccallum wrote:

I thought the "non-electric force" was a density gradient. No??

That's a totally new concept to me.

Density of what?
How is the gradient produced and sustained?
How does it produce a force on the charge-carriers?
What is the governing equation?
Can you cite a reference?

1)
I think that Crawford has the gradient of potential in mind.
The electric potential distribution is due to charges, either
discrete point like charges at specified locations, or charges
distributed in some way, according to a specified charge
density. Electrostatic forces are gradients of Coulomb
potentials.

2)
Aside: An "EMF force" that might (at least macroscopically)
be considered "non electric" is the brute force mechanism of
charge transport employed in a van de Graff generator.

Like Bob, I also talk about a Van de Graff machine as a
possible device to maintain a desired voltage between the
two terminals. When it comes to batteries I say "they are
energy convertors but the input energy is chemical rather
than mechanical." And I do not go any deeper, due to my
limited understanding of chemical cells. My standard joke
is "ask a chemist but do not be surprised if he tells you to
ask a physicist."
Ludwik Kowalski