Thursday, April 20, 2017

electric circuits - How can Ohm's law be correct if superconductors have 0 resistivity?


Ohm's law states that the relationship between current ( I ) voltage ( V ) and resistance ( R ) is


$$I = \frac{V}{R}$$



However superconductors cause the resistance of a material to go to zero, and as I understand it, as $R \to 0$, $I \to \infty$. Does this present a problem for Ohm's law?



Answer



Ohm's law is generally NOT correct, it's called a law for historical reasons only!! It's a law in the same sense in which Hooke's law is a law... it holds only for certain systems under certain conditions, but it's widely known because it's simple and linear!


It's not just superconductors, diodes are a neat everyday example of Ohm's law failing to hold. But it fails for every material under sufficiently extreme circumstances.


Check out this I-V graph for a diode.


Diode I-V graph


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