The flow of electric current through a conductor is governed by Ohm’s Law.
“If temperature and other physical conditions remain the same, the electric current flowing through a conductor is directly proportional to the potential difference between its ends”.
Thus if i be the current flowing through a conductor AB due to the potential difference V = (VA – VB between its ends, then according to Ohm’s law.
V ∝ i
or, V = Ri
where R is the proportionality constant and it is called the resistance of the conductor.
Limitations of Ohm’s Law:
It is found that although Ohm’s law holds good for a large number of materials. There are certain materials and devices for which Ohm’s law isn’t valid.
The materials such as Cu, Al, etc. which Ohms law is valid. V – i curve is linear (straight line) and is called Ohmic conductor.
The materials or devices for which Ohm’s law doesn’t hold well. Either V is not proportional to i and the value of a given V depends upon the sign of V are called non-ohmic conductors.