Ohm's law states that current through a conductor is directly proportional to the voltage across it, provided temperature and other physical conditions will not change. Ohm law can be derived from the following table.
From the table, ratio V/I has a constant value of 10. It is imperative that R for this conductor does not change when V and I both change accordingly.
Directly proportional means, doubling V doubles I, trebling V trebles I and so on.
In mathematical term, Ohm's law can be written as I α V
The other way of mentioning ohm law is that resistance of a conductor does not change so long as physical conditions remain the same.
Conductors which obey ohm's law are usually made of metals, carbons and some alloys. They are referred as ohmic conductors. The conductors not obeying ohmi's law are non ohmic whose resistance changes with voltage and current. The transistors are referred as non ohmic. The characteristic curve for ohmic conductor is shown in the figure.
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