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Re: All Voltage differences are Electrostatic?



Chuck Britton wrote:

As we try to make the transition in class from electrostatics to
'circuits', I try to emphasize that the 1.5 volt potential difference
across the terminals of a 'battery' is EXACTLY the same (except for
magnitude) as the voltage difference that shocks us on cold winter
days, shuffling across the carpet and touching the doorknob.

That's part of the story. Relevant parts include:
-- battery voltage V is lower, as mentioned
-- battery source conductance (1/impedance) is higher
-- battery peak current capability is lower
-- battery energy storage is higher
-- etc.

... most of which can be viewed as differences of
degree, not differences of kind.

It occurred to me that ALL voltage (electrical potential)
differences

As a point of terminology, it is not good to equate
"ALL voltages" with "electrical potential differences".
There exist non-potential voltages.... But based on
context I will assume the intent was to speak of
potential differences only, and defer discussion of
non-potential voltages.

are associated with charge separation - unequal densities of + and -
charges at separated locations. The charges MIGHT not actually be
static but the E field and voltage is the same as if they WERE
static.

That's strictly true; there's no "MIGHT" about it.
If you have a potential, you can find the charge
distribution by applying Laplace's equation.

> (Whatever 'static' might mean at room temperature.)

"Static" means we confine the discussion to
situations where the motion of the charges is
slow compared to all other relevant timescales
in the problem.

In the static limit, all voltages are potentials.

> Of course this wouldn't apply in the least to EMF's.

As a matter of terminology: an EMF is a voltage.
It shows up on a voltmeter just the same as any
other voltage.

Terminology aside, now we are talking about
non-potential voltages.

Yes, non-potential voltages are of a form that
cannot be produced by any static distribution
of charges.