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{{short description|Passive electrical component providin electrical resistance}}{{Infobox electronic component|component=Resistor|image=[[File:Electronic-Axial-Lead-Resistors-Array.png|250px]]|caption=An array of axial-lead resistors|type=[[Passivity (engineering)|Passive]]|working_principle=[[Electric resistance]]|invented=|first_produced=|symbol=[[File:IEEE 315-1975 (1993).2.1.1.a.svg|100px]] [[File:IEEE 315-1975 (1993) 2.1.1.b.svg|100px]]|symbol_caption=IEEE schematic symbols}}A '''reseestor''' is a twa-endit electronic component that maks a [[voltage]] ower its ends evenly tae the circuit's voltage bi [[Ohm's Law]]. In electronic circuits, resistors are uised tae git current flow doun, sort signal levels, tae spleet voltages, bias active elements, an terminate transmission lines, among ither uises. Heigh-power resistors that can dissipate mony [[Watt|watts]] o electrical pouer as heat micht be uised as pairt o motor controls, in pouer distreebution seestems, or as test loads for [[Electric generator|generators]]. Fixed resistors hiv resistances that juist chynge a wee bit wi temperatur, time or operatin voltage. Variable resistors can be uised tae sort circuit elements (sic as a vollum control or a lamp dimmer), or as sensin devices for heat, licht, humidity, force, or chemical acteevity.{{Citation needed}}
Resistors are common elements for electrical networks an electronic circuits and are fun in loads o [[Electronics|electronic equipment]].  Practical resistors as discrete components can be made up o sindry compounds an forms. Resistors are implementit ben integrated circuits an aw.

The electrical function for a resistor is specifeed bi its resistance: common commercial resistors are manufacturt ower a reenge o mair nor nine orders of magnitude. The nominal value for the resistance faws ben the manufacturin tolerance, indicatit on the component.

== Electronic seembols an notation ==
Twa teepical schematic diagram seembol are as fund ablow:<gallery>
File:Resistor,_Rheostat_(variable_resistor),_and_Potentiometer_symbols.svg|ANSI-style: (a)&nbsp;resistor, (b)&nbsp;rheostat (variable resistor), an (c)&nbsp;potentiometer
File:Resistor_symbol_IEC.svg|IEC resistor seembol
</gallery>The notation tae gie a resistor's vailye in a circuit diagram kin be different fae diagram tae diagram.

Ae common scheme is the RKM code follaein IEC 60062. Insteid o uisin a decimal separator, this notation uises a letter loosely associatit wi SI prefixes correspondin wi the pairt's resistance. For exemple, ''8K2''<!-- with uppercase K! --> as pairt merkin code, in a circuit diagram or in a bill of materials (BOM) gies a resistor vailyie for 8.2&nbsp;kΩ. Extrae zeros pit at the end imply a tichter tolerance, for exemple ''15M0'' for three signeeficant digits. Whan the vailyie can be gien wioot needin a prefix (that is, multiplicator 1), an "R" is pit in insteid o the decimal separator. For exemple, ''1R2'' indicates 1.2&nbsp;Ω, an ''18R'' indicates 18&nbsp;Ω.{{Citation needed}}{{Commonscat|Resistors}}

== Theory for operation ==
[[File:ResistanceHydraulicAnalogy2.svg|right|thumb|The [[hydraulic analogy]] compares electric current flowing through circuits to water flowing through pipes. When a pipe (left) is clogged with hair (right), it takes a larger pressure to achieve the same flow of water. Pushing electric current through a large resistance is like pushing water through a pipe clogged with hair: It requires a larger push ([[voltage]]) to drive the same flow ([[electric current]]).<ref>{{cite web|author=Harder, Douglas Wilhelm|title=Resistors: A Motor with a Constant Force (Force Source)|url=https://ece.uwaterloo.ca/~dwharder/Analogy/Resistors/|access-date=9 November 2014|publisher=Department of Electrical and Computer Engineering, University of Waterloo}}</ref>]]

=== Ohm's law ===
{{Main article|Ohm's law}}The behaviour for an ideal resistor is descrived bi [[Ohm's law]]:<math display="block">V=I \cdot R.</math>Ohm's law states thit the [[voltage]] (<math>V</math>) across a resistor is proportional tae the [[Electric current|current]] (<math>I</math>) passin throu it, whaur the constant o proportionality is the resistance (<math>R</math>). For exemple, see gin a 300-ohm resistor is pit across the terminals for a 12-volt battery, than a current for 12 / 300 = 0.04 [[Ampere|amperes]] flowes throu that resistor.

The ohm (seembol: Ω) is the SI unit for electrical resistance, named for [[Georg Simon Ohm]]. An ohm is the same as a [[volt]] per [[ampere]]. As resistors are specifeed an manufacturt ower a muckle reenge o vailyies, the derived units for milliohm (1&nbsp;mΩ = 10<sup>−3</sup>&nbsp;Ω), kilohm (1&nbsp;kΩ = 10<sup>3</sup>&nbsp;Ω), an megohm (1&nbsp;MΩ = 10<sup>6</sup>&nbsp;Ω) are uised commonly an aw.<ref>{{cite book|author=[[American Radio Relay League]] (ARRL)|title=ARRL Handbook for Radio Communications|date=2021|publisher=American Radio Relay League|isbn=978-1-62595-139-7|edition=98|language=en|chapter=Fundamental Theory—Circuits and Components}}</ref><ref name="arrl1968">{{cite book|url=https://archive.org/details/arrl_1968_handbook|title=Radio Amateurs Handbook|date=1968|publisher=American Radio Relay League|editor=Doug DeMaw|edition=45|language=en|chapter=Electrical Laws and Circuits —Resistance}}</ref>{{rp|p.20}}

=== Series an parallel resistors{{anchor|Series_and_parallel_circuits}} ===
{{anchor|series|Series}}

The tot resistance for resistors connectt ane efter the ither is thair individual resistance vailyies pit thegither.{{clear|left}}[[File:Resistors_in_series.svg|alt=Circuit diagram of several resistors, labelled R1, R2 ... Rn, connected end to end]]<math display="block">
R_\mathrm{eq} = R_1  + R_2 + \cdots + R_n.
</math>{{anchor|parallel|Parallel}}<!-- do not delete, used by redirects -->The tot resistance for resistors connectit alangside ane anither is the reciprocal o the reciprocals for the individual resistors pit thegither.<ref name="arrl1968" />{{rp|p.20ff}}{{clear|left}}[[File:Resistors_in_parallel.svg|alt=Circuit diagram of several resistors, labelled R1, R2 ... Rn, side by side, both leads of each connected to the same wires]]<math display="block">
\frac{1}{R_\mathrm{eq}} = \frac{1}{R_1} + \frac{1}{R_2} + \cdots +  \frac{1}{R_n}.
</math>For exemple, a 10 ohm resistor connectit alangside in parallel wi a 5 ohm resistor an a 15 ohm resistor gies oor  {{sfrac|1/10 + 1/5 + 1/15}} ohm o resistance, or {{sfrac|30|11}} = 2.727 ohm.

A resistor netwark thit is a combination o parallel an series connections can be spleet up intae smawer pairts thit are aither ane or the ither. Some complex netwarks o resistors cannae be resolved in this mainer, needin mair sophisticatit circuit analysis. Generally, the Y-Δ transform, or matrix methods can be uised to solve sic problems.<ref>Farago, P.S. (1961) ''An Introduction to Linear Network Analysis'', pp. 18–21, The English Universities Press Ltd.☃☃{{En}}</ref><ref>{{cite journal|author=Wu, F. Y.|year=2004|title=Theory of resistor networks: The two-point resistance|trans-title=Theory for resistor netwarks: The twa-point resistance|journal=Journal of Physics A: Mathematical and General|language=en|volume=37|issue=26|pages=6653–6673|arxiv=math-ph/0402038|bibcode=2004JPhA...37.6653W|doi=10.1088/0305-4470/37/26/004|s2cid=119611570}}</ref><ref>{{cite book|author1=Wu, Fa Yueh|url=https://books.google.com/books?id=H-k8dhB7lmwC&pg=PA489|title=Exactly Solved Models: A Journey in Statistical Mechanics : Selected Papers with Commentaries (1963–2008)|author2=Yang, Chen Ning|date=2009|publisher=World Scientific|isbn=978-981-281-388-6|pages=489–|language=en|trans-title=Exact Solved Models: A Jurney in Statistical Mechanics : Selecit Papers wi Commentaries (1963–2008)}}</ref>

=== Power dissipation ===
At ony instant, the pouer ''P'' (watts) consumed bi a resistor for resistance ''R'' (ohm) is calculatit as:<math display="block">
P = I V = I^2 R =  \frac{V^2}{R}
</math>whaur ''V'' (volts) is the voltage across the resistor an ''I'' (amps) is the [[Ampere|current]] flowin throu it. Uisin [[Ohm's law]], the twa ither forms can be derived. This pouer is convertit intae heat thit haes tae be dissipatit bi the resistor's package afore its temperatur gangs up ower much.<ref name="arrl1968" />{{rp|p.22}}

Resistors are ratit bi the wey o thair maximum pouer dissipation.  Discrete resistors in solid-state electronic seestems are teepically ratit as {{frac|10}}, {{frac|8}}, or {{frac|4}} watt. Thay normally absorb much less not a watt o electrical pouer an arenae needin a lot o tent tae thair pouer ratin.
[[File:Danotherm_HS50_power_resistor.jpg|thumb|An aluminium-encased power resistor rated for dissipation of 50 W when mounted on a heat-sink]]
Pouer resistors are needin tae dissipate substantial amoonts o pouer an are teepically uised in pouer supplies, pouer conversion circuits, an pouer amplifiers; this designation is loosely applied tae resistors wi pouer ratins for 1 watt or mair. Pouer resistors are pheesically mair muckle an mey no uise the preferred vailyies, colour codes, an ooter packages descrived ablow.{{Citation needed}}

See gin the average pouer dissipatit bi a resistor is mair nor its pouer rating, daimige tae the resistor micht happen, permanently chyngin its resistance; this is distinct frae the reversible chynge in resistance due tae its temperatur coefficient whan it warms up. Ower much pouer dissipation micht heeze the temperatur for the resistor tae a pynt whaur it can burn the circuit board or nearbi components, or e'en stairt a fire. Thare are flameproof resistors thit willnae stairt flames wi ony owerload for ony amoont o time.{{Citation needed}}

Resistors micht be specifeed wi heicher ratit dissipation than is gien in service tae tak intae accoont puir air circulation, heich altitude, or high operatin temperatur.

Aw resistors hive a maximum voltage ratin; this micht limit the pouer dissipation for heicher resistance vailyies.<ref>{{cite web|title=Specifications and How to Interpret Them|trans-title=Specifications an Hou tae Interpret Thaim|url=https://seielect.com/news/20170821_-_Resistor_Data_Sheet_Information.pdf|url-status=live|access-date=July 6, 2021|publisher=Stackpole Electronics|language=en}}</ref> For exemple, amang {{frac|4}} watt resistors (an awfy common sort o leaded resistor) ane is listit wi a resistance o 100&nbsp;MΩ<ref>{{Cite web|title=Through Hole Resistor, 0.1 Gohm, RGP Series, 250 mW, ± 5%, Axial Leaded, 750 V|url=https://nl.farnell.com/te-connectivity/rgp0207chj100m/res-100m-5-250mw-axial-thick-film/dp/2805251|url-status=dead|archive-url=https://web.archive.org/web/20210709190647/https://nl.farnell.com/te-connectivity/rgp0207chj100m/res-100m-5-250mw-axial-thick-film/dp/2805251|archive-date=2021-07-09|access-date=2023-10-07|website=nl.farnell.com|language=nl}}</ref> an a maximum ratit voltage o 750&nbsp;V. Hounaiver e'en pittin 750&nbsp;V across a 100&nbsp;MΩ resistor aw the time wad juist hae the ootcome power dissipation for less nor 6&nbsp;mW, makin the nominal {{frac|4}} watt ratin meaninless.{{Citation needed}}
[[File:USSR_power_resistor_VZR_12W.JPG|thumb|VZR power resistor 1.5&nbsp;kΩ 12&nbsp;W, manufactured in 1963 in the Soviet Union]]

== Nonideal properties ==
Practical resistors hiv a series inductance an a smaw parallel [[capacitance]]; these specifications can be important in heich-frequency applications. In a law-noise amplifier or pre-amp, the noise characteristics for a resistor micht be an issue. In some precision applications, the temperatur coefficient for the resistance micht be a concern an aw.{{Citation needed}}

The unwantit inductance, excess noise, an temperatur coefficient are maistly dependent on the technology uised in manufacturin the resistor. They arenae for ordinar specified individually for a parteecular faimily o resistors manufacturt uising a parteecular technology.<ref>A family of resistors may also be characterized according to its ''critical resistance.'' Applying a constant voltage across resistors in that family below the critical resistance will exceed the maximum power rating first; resistances larger than the critical resistance fail first from exceeding the maximum voltage rating. See {{cite book|author=Middleton, Wendy|title=Reference data for engineers: radio, electronics, computer, and communications|author2=Van Valkenburg, Mac E.|publisher=Newnes|year=2002|isbn=0-7506-7291-9|edition=9|pages=5–10|language=en}}</ref> A faimily o discrete resistors micht be characterised bi the wey o its form factor, that is, the size o the device an the poseetion o the leads (or terminals). This is relevant in the practical manufacturin o circuits thit micht uise thaim.{{Citation needed}}

Practical resistors are specified as havin a maximum pouer rating thit is needin tae ootding the anticipatit pouer dissipation for that resistor in a parteecular circuit an aw: this is maistly concernin pouer electronics applications. Resistors wi heicher pouer ratins are pheesically mair muckle an micht need heat sinks. Sometimes in a heich-voltage circuit, the rated maximum wirkin voltage for the resistor needs taen tent. While thare isnae a minimum wirkin voltage for a gien resistor, failure tae accooont for a resistor's maximum ratin micht cause the resistor tae catch fire whan current is ran throu it.{{Citation needed}}

== References ==
{{Reflist}}
[[Category:Electrical components]]
[[Category:Resistive components]]