Ohm's law states that the electric current flowing through a conductor is directly proportional to the potential difference across its two ends, when other physical conditions like temperature etc., remain constant.
i.e., or
$\mathrm{V}\propto \mathrm{I}$

$\mathrm{V}=\mathrm{IR}$
or
Thus, the ratio $\mathrm{V}:\mathrm{I}$ is a constant. This constant is called the resistance (R) of the conductor. Circuit diagram for Ohm's law :If a graph is drawn between the potential difference (V) and current (I), the graph is found to be a straight line passing through the origin. This shows that the current is directly proportional to the potential difference. Thus, the ratio $\frac{\mathit{V}}{\mathit{I}}$ remains constant. This constant is called the resistance of the conductor. The gradient of the straight line graph is related to the resistance $\left(\mathit{R}\right)$ of the conductor.