Limitations of Ohm’s Law
Ohm’s law has been found valid over a large class of materials, there do exist materials and devices used in electric circuits where the proportionality of V and I does not hold.
Such conductor are called non Ohmic conductors. The deviations broadly are one or more of the following type V ceases to be proportional to I
The relation between V and I depends on the sign of V.
In other words, if I is the current for a certain V, then reveres the direction of V keeping its magnitude fixed, does not produce a current of the same magnitude as I in the opposite direction.
Ohm's law is not a fundamental law of nature. There are a number of commonly used circuit elements which do not obey this law. They have one or more of the following properties:
1. V depends on I non-linearly.
2. The relationship between V and I depends on the sign of V for the same absolute value of V.
3. The relation between V and I is non-unique, that is, for the same current I, there is more than one value of voltage V.
