A current-potential difference graph (also known as an I-V graph) shows how the current passing through a component varies with the potential difference. The graph has:
A conductor that obeys Ohm’s law has a constant resistance. The line is straight, passing through the origin. which shows tells us that the current is proportional to the potential difference across the resistor, at a constant temperature.
Examples of non-ohmic components are lamps, diodes, light-dependent resistors (LDRs) and thermistors. They do not have a constant resistance, the resistance changes as the current passing across the component changes.
Below is the graph for a filament bulb.
The graph for the filament bulb does not obey Ohm’s law as the graph is not a straight line. The metal filament gets hotter as current flows through it. The metal atoms in the filament vibrate more intensely, which increases the collisions with metal atoms and passing electrons. This leads to an increase in resistance, curving the graph.
The reason the graph is symmetrical is that the relationship does not change when the current flows in the opposite direction.
Below is the current-potential graph for a diode.
As the graph is not a straight line, it does not obey Ohm’s law. As diodes have a high resistance in one direction they only let current flow in one direction.