Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: R = V/I ?



At 15.09 06/05/00 -0500, Rick Tarara wrote:
If one wants to stay within the 'philosophy' that resistance is a
temperature and geometry dependent property of the material, then what one
would say is that the light bulb has a well-defined resistance for every
temperature encountered within a given range of currents. The I-V graph is
then a convenient way to MEASURE this resistance. ;-)

This is OK if indeed you want to *define* an electrical parameter in terms
of temperature and geometry (I wouldn't in this instance), but notice what
Leigh is saying:

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.

Mark


From: "Mark Sylvester" <msylvest@SPIN.IT>
>
> But Leigh, would you not say that the (by now overworked) lightbulb has a
> well-defined resistance given by R = V/I at every point on the I-V graph?
>
> Mark
>


_____________________________________
Mark Sylvester
United World College of the Adriatic,
34013 Duino TS, Italy.
_____________________________________