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 and passes through the origin. This shows that the current is proportional to the potential difference across the resistor, provided the temperature remains constant.
Examples of non-ohmic components are lamps, diodes, light-dependent resistors (LDRs) and thermistors. They do not have constant resistance; the resistance changes as the current passing through the component changes.
Below is the current-potential difference graph for a filament bulb.
The graph for the filament bulb does not obey Ohm’s law because it 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 number of collisions with 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 difference graph for a diode.
As the graph is not a straight line, it does not obey Ohm’s law. Diodes have high resistance in one direction, allowing current to flow only in that direction.