Resistors are one of the most common components in electronics, if not the most common components. They have a specific resistance that is very useful for a wide variety of reasons. They have varying values of resistance, from milliohms to megaohms, as well as different packages from tiny surface mount devices that you can barely see up to large chassis mounted packages that can handle thousands of watts of power. They also have varying precisions, from guaranteeing to be only within 10% of the stated value to .01% precision. Of course, higher precision costs more, so there’s always a trade-off.
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of electrical power as heat, may be used as part of motor controls, in power distribution systems, or as test loads for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds and forms. Resistors are also implemented within integrated circuits.
The electrical function of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. The nominal value of the resistance falls within the manufacturing tolerance, indicated on the component.