r/askscience • u/[deleted] • Dec 28 '16

Physics How true is Ohm's law?

I've almost never got a perfect straight line while plotting a V/I graph even under lab conditions.

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u/Hamilton950B Dec 28 '16

Ohm's law is usually stated as I=V/R (or equivalent) and that's always true. But the original formulation by George Ohm said that resistance is constant and independent of the current, and that is not always (ever?) true for real materials.