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Besides the fact that one does not following Ohm's law, are there any other differences between these conductors?

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closed as too broad by Ignacio Vazquez-Abrams, uint128_t, PeterJ, placeholder, Bence Kaulics May 29 '16 at 20:00

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  • \$\begingroup\$ "Non-ohmic" covers a wide variety of devices and behaviors, so while there are other differences there are far too many to list in an appropriate amount of space. \$\endgroup\$ – Ignacio Vazquez-Abrams May 29 '16 at 4:50
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All non-ohmic means is that the V and I relationship does not follow Ohm's Law.

Be aware that this is more a description of their behaviour, than a definition of what they are. And conductors that are described as ohmic in one context may be called non-ohmic in another.

A diode is perhaps the classic non-ohmic device, others include filament light bulbs, electrochemical cells, electric arcs. You will note that the short list of conductors here includes a semi-conductor, a metal, a liquid and a gas/plasma, so non-ohmic is hardly a definition of the conductor.

A filament light bulb is interesting, because as its temperature varies from 300K to 3000K, the resistance varies by more than a factor of 10, very non-linear / non-ohmic indeed.

This non-linear resistance trait is shared by most metals, however we don't usually notice it. For instance a copper cable's resistance increases by 0.4% per degree, much the same as tungsten. But we tend to call copper 'ohmic' as we typically to use it to carry currents that don't heat it up much (if your mains extension lead is warm to the touch, then maybe it's close to being overloaded), but tungsten filaments 'non-ohmic' as their normal use is over a much wider range.

It's their behaviour, and whether we define 'follow Ohm's Law' to mean within 1% or 10% or 0.01% accuracy.

But I think everyone without exception would call a diode 'non-ohmic'.

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All conventional resistors are, at some level, non-ohmic. Ohm's Law states that current is proportional to voltage, and if nothing else this will fail at some applied high voltage, when the material suffers dielectric breakdown and turns into an arc.

Furthermore, as Neil_UK has mentioned, the voltage/current ratio will be affected by temperature. This is not ordinarily an issue: such a resistor will (over some useful voltage/current range) exhibit an instantaneous V/I ratio which is constant for a given temperature. The effects of heating are generally treated as a modification of the ratio. This is ordinarily a useful approach since for high speed circuits (say, audio or higher) temperature effects ordinarily change more slowly than the signal.

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