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]]