Ohm’s Law: The current flowing through a conductor is directly proportional to the voltage applied to across the ends of the conductor.So, the V-I graph for a conductor following the Ohm’s law is a straight line with a positive slope.
Limitations of this law:
1. Now, this law is valid for conductors only and that too at a constant temperature. The resistance of a conductor increases with temperature. Hence, for changing temperature the V-I graph for a conductor will be non-linear (not a straight line).
2. In case of insulators ohm’s law is not followed at all, insulators do not conduct at all. But, when a very high voltage is applied across an insulator dielectric break down occurs and all of a sudden current begins to flow.
3. Ohm’s law is not followed by semiconductors. The V-I graph has a steep rising at a particular voltage, which indicates that the material begins to conduct properly only after a certain voltage.
Hope this explanation helps you understand the limitations of the Ohm’s Law.
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