A resistor is a passive two-terminal component that implements resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor’s terminal. This relationship is represented by Ohm’s law:

I = V/R

The ratio of the voltage applied across a resistor’s terminal to the intensity of the current in the circuit is called its resistance, and this can be assumed to be a constant for ordinary resistors working within their ratings.

Resistors are common elements of electrical networks and electronic circuits. They are ubiquitous in electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire. They can also be implemented within integrated circuits, particularly analog devices. Also they can be integrated into hybrid and printed circuits.

The functionality of a resistor is specified by its resistance. It is common for commercial resistors to range more than nine orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention of the manufacturing tolerance of the chosen resistor. This is according to its specific application.

Practical resistors have a series inductance and a small parallel capacitance. These specifications are important in high-frequency applications. The unwanted inductance, excess noise and temperature coefficients are dependent on the technology used in manufacturing the resistor. They are not typically specified individually for a particular family of resistors.