Verified experimentally Ohm’s law states that the current flowing through a conductor is proportional to the voltage V across its ends when its physical conditions (temperature etc.) remains unchanged Expressed mathmatically we can write.
V/I = R (Constant of proportionally)
The constant R is known as the resistance of the conductor.
Ohm’s law, a experimental law is valid only for metallic conduction. We now know that there are quite a number of substances (e.g. semi conductors) for which Ohm’s law is not always valid. For such cases the current voltage graphs are not linear. We illustrate this point by showing the plot of current voltage graph for some interesting cases
