Resistors required to dissipate substantial amounts of power, particularly used in power supplies, power conversion circuits, and power amplifiers, are generally referred to as power resistors this designation is loosely applied to resistors with power ratings of 1 watt or greater. : p.20 Series and parallel resistorsĪn aluminium-encased power resistor rated for dissipation of 50 W when mounted on a heat-sink Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 mΩ = 10 −3 Ω), kilohm (1 kΩ = 10 3 Ω), and megohm (1 MΩ = 10 6 Ω) are also in common usage. An ohm is equivalent to a volt per ampere. The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. For example, they have inductance and capacitance, which affect the relation between voltage and current in alternating current circuits. In practice, resistors deviate from the ideal behavior given by Ohm's law. For example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a current of 12 / 300 = 0.04 amperes flows through that resistor. The nominal value of the resistance falls within the manufacturing tolerance, indicated on the component. 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. Resistors are also implemented within integrated circuits. Practical resistors as discrete components can be composed of various compounds and forms. Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. 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. 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.įixed resistors have resistances that only change slightly with temperature, time or operating voltage. 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.

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element.

220k ohm resistor color code