State and Explain Ohm’s Law and its limitations

Ohm’s Law:

The flow of electric current through a conductor is governed by Ohm’s Law.

Statement:

“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 = (V_A – V_B 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.