Ohm's Law states that if a conductor is at a constant temperature, the current flowing through the conductor is directly proportional to the voltage(potential difference) across it. This means that if we plot voltage on the x-axis of a graph and current on the y-axis of the graph, we will get a straight-line.

The gradient of the straight-line graph will be related to the resistance of the conductor as:

I/V=1/R , where I,V and R are current, voltage and resistance respectively at a constant temperature.