Ohmic

Ohmic describes a component or material that follows Ohm's law, displaying a linear relationship between voltage and current. In an ohmic device the current I through the component is proportional to the voltage V across it, such that V = IR, where R is the resistance. The key feature is that R remains effectively constant as V and I vary within the operating range.

This behavior requires constant temperature and a material whose resistivity does not change significantly with current. In practice, many metals at room temperature behave approximately ohmically for modest voltages and currents, and electrical resistors are designed to be ohmic within their specified tolerances.

Devices that do not exhibit a constant resistance are non-ohmic. Examples include diodes, transistors in certain regions of operation, varistors, and many non-linear devices. A filament lamp is another classic non-ohmic element because its resistance increases as it heats up, causing its V–I curve to bend.

In alternating current circuits, a pure ohmic resistor presents an impedance equal to its resistance, independent of frequency, although real components may exhibit parasitic effects at high frequencies or with temperature changes.

Origin of the term: ohmic derives from Ohm, Georg Simon Ohm, who formulated Ohm's law in the early 19th century.