Re: R = V/I ?

[Leigh Palmer <palmer@SFU.CA>]

> At 11.38 05/05/00 -0700, Leigh Palmer wrote:
> > I've never considered R = V/I to be anything so general as the
> > definition of a physical quantity. It is the definition (with
> > Ohm's law implicit) of a parameter which we call the resistance.
> > This parameter may apply to many two-terminal devices, notably
> > to resistors, and it is inappropriate to apply it to devices
> > which do not obey Ohm's law.
>
> He has just recently made a strong case for considering a lightbulb to be
> "a device which does not obey Ohm's law". It seems to follow that it is
> inappropriate to speak of the electrical resistance of a lightbulb. This
> seems to be an idiosyncratic position to take, and I'm interested to see
> how he will extricate himself from this corner.

Please explain the corner I'm in. I believe I implied it is not
appropriate to describe light bulbs by their resistance as they
do not behave like resistors. A VI characteristic is necessary
to describe their behaviour in circuits.

(An aside: the first instrument ever made by Hewlett Packard was
an audio oscillator based on a Wien Bridge, a circuit which uses
two nonlinear light bulbs as circuit elements. They made several
of these for Walt Disney to use in the making of "Fantasia".  A
digression from the aside: "Fantasia" was the first movie I ever
saw. I saw it in first run, and I remember the experience.)

Leigh