A diode is considered non-ohmic in a circuit because its current-voltage relationship is nonlinear. Unlike ohmic devices such as resistors, which follow Ohm’s law (where current is directly proportional to voltage), a diode exhibits a different behavior. Specifically, a diode allows current to flow in one direction (forward biased) with very little resistance once a certain voltage threshold is reached (forward voltage drop), while in the opposite direction (reverse biased), it blocks current almost completely.

The non-ohmic nature of a diode stems from its characteristic current-voltage relationship, which is highly dependent on the diode’s internal structure and semiconductor material properties. Ohmic devices, like resistors, maintain a linear relationship between current and voltage across a wide range of operating conditions. In contrast, diodes exhibit a nonlinear relationship due to the way charge carriers behave within the semiconductor material, particularly near the junction where current flows predominantly in one direction under forward bias.

A circuit is considered non-ohmic when it contains components, such as diodes, whose current-voltage characteristics do not adhere to Ohm’s law. In such circuits, the behavior of current flow and voltage drop across components like diodes is nonlinear and depends on factors such as the component’s intrinsic properties, operating conditions, and biasing.

Diodes do not obey Ohm’s law primarily because their current-voltage relationship is not linear. Ohm’s law states that the current through a conductor between two points is directly proportional to the voltage across the two points. However, a diode’s current does not increase linearly with voltage; instead, it shows an exponential relationship under forward bias and blocks current under reverse bias. Therefore, the application of Ohm’s law to a diode’s behavior would not accurately predict its current-voltage characteristics.

A diode is a semiconductor device. The term “non-ohmic” refers to its characteristic current-voltage relationship, which deviates from the linear behavior described by Ohm’s law. Diodes are made from semiconductor materials like silicon or germanium, where the movement of charge carriers (electrons and holes) across the junction determines its conductivity properties. This semiconductor nature is fundamental to understanding why diodes exhibit non-ohmic behavior in electrical circuits.