Re: R = V/I ?

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

Leigh Palmer wrote:
> .... 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. ...

I see two terms here, resistance (presumably the V/I ratio under
specified conditions) and resistor (presumably a device in which
V/I remains practically constant). In that context all is in order.
A light bulb is not a resistor but it has a well defined R when the
conditions are specified, for example, when I= 1A and V=100V.
What can be more simple than this? Measuring V/I ratios for
different I and V (light bulbs, wire rheostat, etc.) is a good old
activity for students.

The apparent disagreements seem to be centered on what should
be called Ohm's law. Right? Is it a law of nature or a low of
devices. A device operating under specific conditions is said to
obey Ohm's law when V/I remains constant. Ohm's law is a
very useful idealization. It can also be expressed as a relation
of proportionality between the current density j (in a wire) and
E responsible for the drift of charges.
Ludwik Kowalski