state ohms law and write the condition in which law is beyed?

Ohm’s law states that the current (I) flowing through a conductor is directly proportional to the potential difference (V) across the ends of a conductor, provided physical conditions of the conductor such as temperature, mechanical strain etc. are kept constant.

V ∝  I

On removing the proportionality signs we get:

V = IR

Where R is the resistance and is measured in SI unit called ohm(Ω).

Since according to ohm’s law V is directly proportional to I , Therefore the graph has to be a straight line. This straight line hence also indicates that Resistance is a constant quantity throughout.

Graph of Ohm’s law is a straight line obtained when current in the circuit (I) is plotted along x axis and potential (V) along y 

axis.