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] |
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