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The value of r was expected to be the same for
all currents, in the range for which the power
supply was designed.
different for different currents.
Terminology point: On the side of the tracks
where I grew up, "resistance" means the small-signal
resistance,
R := dV/dI
as discussed at
http://www.av8n.com/physics/resistance.htm
I am beginning to suspect that Ludwik might have
been using some other definition of R.
Ludwik Kowalski wrote:
The value of r was expected to be the same for
all currents, in the range for which the power
supply was designed.
Why should we expect that? Ohm's law is not a
God-given law of nature.
> But it turned out to be
different for different currents.
I'm not surprised.
> Nowhere in our
textbooks was this possibility mentioned.
The textbook assumes that everything in the world
is ohmic? You need a better textbook, stat.
> Many numerical problems would make no
sense if r were current-dependent.
The real world would not make sense if everything
were ohmic.
> What is
wrong with testing this experimentally? What
is wrong with asking how r depends on I?
Nothing wrong. Excellent idea, actually.
How to explain the observed dependance?
Draw the (I,V) curve.