Re: R = V/I ?

[Leigh Palmer <palmer@SFU.CA>]

At 11:01 AM -0700 5/8/00, Mark Sylvester wrote:
> I think the reason why this is indeed pretty crazy is that the resistance
> of a device is the property which causes it to dissipate energy (if I may
> use the expression) when there is a current in it. (This is the physical
> meaning of resistance, regardless of whether the device is ohmic or not.)
> When emf's are introduced then there are other energy conversion processes,
> and V/I is no longer linked to *dissipation*.

I now understand why Mark approaches his laboratory exercise in the
manner he does. It is because of this rather unconventional view of
the meaning of resistance. I would not say that the resistance of a
resistor is the property of the device which causes it to dissipate
energy, but that is just a different world view, I guess. My amateur
radio background makes me think of resistance in a different way.

If I were to plug a Mixmaster into the wall and use it to stir cake
batter, then the system would be dissipating energy. One could
calculate a resistance R = V/I, and I^2 R would, indeed be the
dissipated power. Could one usefully threat the mixmaster and cake
batter system as having a resistance R? Not in my world view. Many
such example come to mind, and I would rather reserve the concept
of resistance to those devices which obey Ohm's law*.

Leigh

*The Mixmaster-cake batter system does not obey Ohm's law. Even if
it did I would be reluctant to ascribe to it a resistance.