Ohm 4462484 225808390 2008-07-15T14:32:47Z Binksternet 4967956 [[WP:UNDO|Undid]] revision 225793656 by [[Special:Contributions/213.83.85.131|213.83.85.131]] ([[User talk:213.83.85.131|talk]])List of font equivalents should be more than just MS Word {{otheruses4|the [[SI]] derived unit|other meanings|Ohm (disambiguation)}} [[Image:Electronic multi meter.jpg|thumb|250px|A [[multimeter]] can be used to measure resistance in ohms. It can also be used to measure capacitance, voltage, current, and other electrical characteristics.]] [[Image:Aeldre kulmassemodstande.jpg|thumb|Several [[resistor]]s. Their resistance, in ohms, is marked using a [[Electronic color code|color code]].]] The '''ohm''' (symbol: [[Ω]]) is the [[SI]] unit of [[electrical impedance]] or, in the [[direct current]] case, [[electrical resistance]], named after [[Georg Ohm]]. == Definition == The ohm is the electric resistance between two points of a conductor when a constant potential difference of 1 [[volt]], applied to these points, produces in the conductor a current of 1 [[ampere]], the conductor not being the seat of any [[electromotive force]].<ref>[http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf BIPM SI Brochure: Appendix 1, p. 144]</ref> :<math>\Omega = \dfrac{\mbox{V}}{\mbox{A}} = \dfrac{\mbox{m}^2 \cdot \mbox{kg}}{\mbox{s}^{3} \cdot \mbox{A}^2}</math> == Conversions == *A measurement in ohms is the reciprocal of a measurement in [[siemens (unit)|siemens]], the [[SI]] unit of [[electrical conductance]]. Note that 'siemens' is both [[Grammatical number|singular]] and [[plural]]. The non-SI unit, the [[mho]] (ohm written backwards), is equivalent to siemens but is mostly obsolete and rarely used. *Ohms to watts: The power dissipated by a resistor may be calculated using resistance and voltage. The formula is a combination of [[Ohm's law]] and [[Joule's law]]: ::<math>P={V^2 \over R}</math> :where P is the power in watts, R is the resistance in ohms and V is the voltage across the resistor. :This method is not reliable for determining the power of an [[incandescent light bulb]], resistance heater or electric short since all these devices operate at high temperatures and the resistance measured using a meter will not represent the operating resistance. For these conditions instead multiply V by current in [[amperes]] to get power in [[watt]]s. ==References and notes== <references/> == See also == * [[Ohm's law]] * [[Resistor]] * [[Resistivity]] * [[abohm]] == External links == *[http://www.fh-nuernberg.de/institutionen/bibliothek/bibsuche/texte_online_aufrufen/historische_buecher_der_gso_fh/werke_von_georg_simon_ohm/ Scanned books of Georg Simon Ohm at the library of the University of Applied Sciences Nuernberg] * [http://www.bipm.fr/en/si/si_brochure/ Official SI brochure] * [http://physics.nist.gov/Pubs/SP811/contents.html NIST Special Publication 811] * [http://www.sizes.com/units/ohm.htm History of the ohm at sizes.com] [[Category:SI derived units]] [[Category:Units of electrical resistance]] [[ar:أوم]] [[ast:Ohmiu]] [[be:Ом (адзінка вымярэння)]] [[be-x-old:Ом]] [[bs:Om]] [[br:Ohm]] [[bg:Ом]] [[ca:Ohm]] [[cs:Ohm]] [[da:Ohm]] [[de:Ohm]] [[el:Ωμ (μονάδα μέτρησης)]] [[es:Ohmio]] [[eo:Omo]] [[eu:Ohm]] [[fa:اهم]] [[fr:Ohm (unité)]] [[gl:Ohm]] [[ko:옴 (단위)]] [[hi:ओह्म]] [[hr:Om]] [[id:Ohm]] [[is:Óm]] [[it:Ohm]] [[he:אוהם]] [[lv:Oms]] [[li:Ohm (eenheid)]] [[nl:Ohm (eenheid)]] [[ja:オーム]] [[no:Ohm]] [[nn:Ohm]] [[pl:Om (jednostka)]] [[pt:Ohm]] [[ro:Ohm]] [[ru:Ом]] [[sk:Ohm (jednotka)]] [[sl:Om]] [[sr:Ом (јединица)]] [[fi:Ohmi]] [[sv:Ohm]] [[th:โอห์ม]] [[vi:Ohm]] [[tr:Ohm]] [[uk:Ом]] [[zh:歐姆]]