Re: Internal resistance

[John Denker <jsd@AV8N.COM>]

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.