As per the question there are two ohmic devices.
The first ohmic device is a good conductor and the second one is a good insulator.
As per Ohm's law the current flowing through a conductor is directly proportional to the potential difference maintained across the two ends of a conductor at constant temperature and pressure. If V is the potential and I is the current flow through these Ohmic devices,then mathematically it can be written as-
V∝ I [ at constant temperature and pressure]
⇒V= IR
Here R is the proportionality constant called resistance of the material.
Hence the resistance R is calculated as -
Now a graph is plotted taking potential V on X-axis and current I along Y- axis.
The graph will be a straight line for conductor and will be a curve depending on the type of insulator.
The slope of this graph will give the resistance of the material.
An insulator is a substance through which current flow is very low as its resistance is very high.Hence the slope of the V-I curve is very large.
A conductor is that substance through which current is flown easily as the resistance of conductor is very low.Hence the slope of V-I curve is smaller,