Re: Internal resistance again.

[Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU>]

JohnM asked:  "Have you tried squeezing nothing
between your plates?"

Yes, but only for Al. The voltage at zero current
(EMF) was 1.45 V. I did not measure the EMF
with the Ti foil; the current will be flowing through
it for many weeks. Let me add that these are side
observations; I want a stable current and I get it.
In other words the power supply does what I want.

In this simple circuit the voltmeter should show
I*R, no matter what happens inside the power
supply. But it does not; V is not proportional to I.

> I am using a d.c. power supply to pass a current
> through an Al foil. From the positive of the power
> supply the current goes through the ammeter
> and through the foil (firmly squeezed between
> two metallic plates). The voltage is measured
> between these plates. I expected voltage to be
> I*R but it is not.
>
> I=1.3 A  --> 0.55 volts
> I=2.0 A --> 1.06 volts
> I=2.9 A --> 1.30 volts
>
> How can this be explained? I am sure that R
> is essentially constant. The impedance of the
> voltmeter is certainly much larger than 1 ohm.
> Ludwik Kowalski