The terms linear and nonlinear describe the dependence of voltage, current and resistance of components or circuits:
- Linear Elements/Circuits:
- A component or circuit is said to be linear if the relationship between current and voltage follows Ohm’s Law (i.e., V=IRV = IRV=IR).
- In linear components, the current is directly proportional to the applied voltage, and resistance (or impedance) remains constant regardless of the voltage or current levels.
- Examples include resistors and inductors (in ideal conditions) where the current increases or decreases proportionally with the voltage.
A linear relationship is graphically denoted by a straight-line when voltage is plotted versus current (V-I characteristics).
- Nonlinear Elements/Circuits:
- A circuit or component is nonlinear when the voltage versus current relation is not that of a direct proportion, that is, when the resistance varies with the applied voltage or current.
- The current in nonlinear components does not rise in direct proportion to the applied voltage, and the resistance or impedance changes under conditions temperature, light, or even the current magnitude.
- Examples are diodes, transistors and light bulbs. An example is a diode, which conducts in one direction only, and which is nonlinear because the current grows exponentially with voltage beyond some threshold (forward voltage).
Graphically, a nonlinear relationship will produce a curve when a graph of voltage versus current (V-I characteristics) is made, indicating that the current varies nonlinearly with the voltage.