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] |
I had a look at the textbooks in my office to check on how they approach
the question:
PSSC, Project Physics and Hecht take Leigh's line, defining resistance only
in the context of Ohm's Law.
Giancoli explicitly acknowledges both views.
Halliday & Resnick define R as V/I, and don't mention Ohm's Law for another
5 pages (this was my first undergraduate text, so maybe this is where my
view comes from).
Most interestingly, the 5 British A-level books that I have (Breithaupt,
Duncan, Whelan & Hodgeson, Cackett Lowrie & Steven, and a brand new one by
Dobson Grace & Lovett) all define resistance as R = V/I and then later
introduce Ohm's Law. The last one even introduces the concept as
"Resistance is the electrical property of a material that makes moving
charges dissipate energy" in bold type.
I quote this only in response to Leigh's classification of my view as
"unconventional".
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 treat the mixmaster and cake
batter system as having a resistance R? Not in my world view. Many
such examples come to mind, and I would rather reserve the concept
of resistance to those devices which obey Ohm's law*. [corrected]
Yes, but an electric motor in the first place does work, and is not a
dissipative device, so I'm not convinced by this example. It does remind me
that the real and imaginary axes on a phasor diagram are usually labelled
"resistance" and "reactance". Presumably you would want to use some other
word than resistance here, since the phasor diagram could well apply to the
Mixmaster.