The discussion on the California Science Framework has reminded me that I am a bit confused about Ohm's law and the meaning of "Ohmic".
As I understand it, incandescent light bulbs are considered "non-ohmic" because the current will not vary in direct proportion to the voltage applied.
As I understand Ohm's law, it states that the current is directly proportional to the applied voltage, but only if the resistance remains constant.
The filament of the incandescent bulb (again, as I understand it) depends on its dimensions (length, cross-sectional area), type of material (tungsten?) and the temperature.
Since the filament gets significantly hotter as current flows through it, its resistance changes significantly and thus "I" will not vary directly with "V".
But does this make it "non-ohmic"?
If we could somehow couple the filament to a heat sink so that the temperature of the filament does not change with the increasing voltage would "I" then vary directly with "V"? (...and would it then be "Ohmic"?)
Other materials that are considered "ohmic" will not have "I" and "V" vary directly if we allowed their resistance to somehow vary. In light bulbs is it because the change in resistance is brought about directly as a result of the application of a potential difference that they are considered "non-Ohmic"? Still, what if the temperature were held fixed? If the filament is then considered "ohmic", it seems to be an artificial distinction.
Aren't there other materials whose resistance changes with voltage even without a change in geometry, type o' material or temperature?
Thanks for any "light" you can shed on this subject.
Stu Leinoff
(P.S.
As a "lurker" I subscribe to the digest version of the list server. I apologize in advance if I appear non responsive)
Stuart Leinoff
Professor of Physics
Science Division Chair
ACC