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class="vector-toc-numb">2</span> <span>Relation to conductance</span> </div> </a> <ul id="toc-Relation_to_conductance-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Power_as_a_function_of_resistance" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Power_as_a_function_of_resistance"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Power as a function of resistance</span> </div> </a> <ul id="toc-Power_as_a_function_of_resistance-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-History" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#History"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>History</span> </div> </a> <button aria-controls="toc-History-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle History subsection</span> </button> <ul id="toc-History-sublist" class="vector-toc-list"> <li id="toc-Historical_units_of_resistance" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Historical_units_of_resistance"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>Historical units of resistance</span> </div> </a> <ul id="toc-Historical_units_of_resistance-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Realization_of_standards" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Realization_of_standards"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Realization of standards</span> </div> </a> <ul id="toc-Realization_of_standards-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Symbol" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Symbol"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Symbol</span> </div> </a> <ul id="toc-Symbol-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Notes_and_references" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Notes_and_references"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>Notes and references</span> </div> </a> <ul id="toc-Notes_and_references-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Ohm</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 89 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-89" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">89 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-af mw-list-item"><a href="https://af.wikipedia.org/wiki/Ohm" title="Ohm – Afrikaans" lang="af" hreflang="af" data-title="Ohm" data-language-autonym="Afrikaans" data-language-local-name="Afrikaans" class="interlanguage-link-target"><span>Afrikaans</span></a></li><li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%A3%D9%88%D9%85" title="أوم – Arabic" lang="ar" hreflang="ar" data-title="أوم" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-as mw-list-item"><a href="https://as.wikipedia.org/wiki/%E0%A6%93%E0%A6%AE" title="ওম – Assamese" lang="as" hreflang="as" data-title="ওম" data-language-autonym="অসমীয়া" data-language-local-name="Assamese" class="interlanguage-link-target"><span>অসমীয়া</span></a></li><li class="interlanguage-link interwiki-ast mw-list-item"><a href="https://ast.wikipedia.org/wiki/Ohmiu" title="Ohmiu – Asturian" lang="ast" hreflang="ast" data-title="Ohmiu" data-language-autonym="Asturianu" data-language-local-name="Asturian" class="interlanguage-link-target"><span>Asturianu</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/Om_(%C3%B6l%C3%A7%C3%BC_vahidi)" title="Om (ölçü vahidi) – Azerbaijani" lang="az" hreflang="az" data-title="Om (ölçü vahidi)" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bn mw-list-item"><a href="https://bn.wikipedia.org/wiki/%E0%A6%93%E0%A6%B9%E0%A6%AE" title="ওহম – Bangla" lang="bn" hreflang="bn" data-title="ওহম" data-language-autonym="বাংলা" data-language-local-name="Bangla" class="interlanguage-link-target"><span>বাংলা</span></a></li><li class="interlanguage-link interwiki-be mw-list-item"><a href="https://be.wikipedia.org/wiki/%D0%9E%D0%BC_(%D0%B0%D0%B4%D0%B7%D1%96%D0%BD%D0%BA%D0%B0_%D0%B2%D1%8B%D0%BC%D1%8F%D1%80%D1%8D%D0%BD%D0%BD%D1%8F)" title="Ом (адзінка вымярэння) – Belarusian" lang="be" hreflang="be" data-title="Ом (адзінка вымярэння)" data-language-autonym="Беларуская" data-language-local-name="Belarusian" class="interlanguage-link-target"><span>Беларуская</span></a></li><li class="interlanguage-link interwiki-be-x-old mw-list-item"><a href="https://be-tarask.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Belarusian (Taraškievica orthography)" lang="be-tarask" hreflang="be-tarask" data-title="Ом" data-language-autonym="Беларуская (тарашкевіца)" data-language-local-name="Belarusian (Taraškievica orthography)" class="interlanguage-link-target"><span>Беларуская (тарашкевіца)</span></a></li><li class="interlanguage-link interwiki-bg mw-list-item"><a href="https://bg.wikipedia.org/wiki/%D0%9E%D0%BC_(%D1%84%D0%B8%D0%B7%D0%B8%D0%BA%D0%B0)" title="Ом (физика) – Bulgarian" lang="bg" hreflang="bg" data-title="Ом (физика)" data-language-autonym="Български" data-language-local-name="Bulgarian" class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-bo mw-list-item"><a href="https://bo.wikipedia.org/wiki/%E0%BD%A8%E0%BD%BC%E0%BC%8B%E0%BD%98%E0%BD%B4%E0%BC%8D" title="ཨོ་མུ། – Tibetan" lang="bo" hreflang="bo" data-title="ཨོ་མུ།" data-language-autonym="བོད་ཡིག" data-language-local-name="Tibetan" class="interlanguage-link-target"><span>བོད་ཡིག</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/Om" title="Om – Bosnian" lang="bs" hreflang="bs" data-title="Om" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-br mw-list-item"><a href="https://br.wikipedia.org/wiki/Ohm" title="Ohm – Breton" lang="br" hreflang="br" data-title="Ohm" data-language-autonym="Brezhoneg" data-language-local-name="Breton" class="interlanguage-link-target"><span>Brezhoneg</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Ohm_(unitat)" title="Ohm (unitat) – Catalan" lang="ca" hreflang="ca" data-title="Ohm (unitat)" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cv mw-list-item"><a href="https://cv.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Chuvash" lang="cv" hreflang="cv" data-title="Ом" data-language-autonym="Чӑвашла" data-language-local-name="Chuvash" class="interlanguage-link-target"><span>Чӑвашла</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/Ohm" title="Ohm – Czech" lang="cs" hreflang="cs" data-title="Ohm" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-cy mw-list-item"><a href="https://cy.wikipedia.org/wiki/Ohm" title="Ohm – Welsh" lang="cy" hreflang="cy" data-title="Ohm" data-language-autonym="Cymraeg" data-language-local-name="Welsh" class="interlanguage-link-target"><span>Cymraeg</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Ohm" title="Ohm – Danish" lang="da" hreflang="da" data-title="Ohm" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Ohm" title="Ohm – German" lang="de" hreflang="de" data-title="Ohm" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/Oom" title="Oom – Estonian" lang="et" hreflang="et" data-title="Oom" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-el mw-list-item"><a href="https://el.wikipedia.org/wiki/%CE%A9%CE%BC_(%CE%BC%CE%BF%CE%BD%CE%AC%CE%B4%CE%B1_%CE%BC%CE%AD%CF%84%CF%81%CE%B7%CF%83%CE%B7%CF%82)" title="Ωμ (μονάδα μέτρησης) – Greek" lang="el" hreflang="el" data-title="Ωμ (μονάδα μέτρησης)" data-language-autonym="Ελληνικά" data-language-local-name="Greek" class="interlanguage-link-target"><span>Ελληνικά</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Ohmio" title="Ohmio – Spanish" lang="es" hreflang="es" data-title="Ohmio" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Omo_(mezurunuo)" title="Omo (mezurunuo) – Esperanto" lang="eo" hreflang="eo" data-title="Omo (mezurunuo)" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target"><span>Esperanto</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/Ohm" title="Ohm – Basque" lang="eu" hreflang="eu" data-title="Ohm" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%A7%D9%87%D9%85" title="اهم – Persian" lang="fa" hreflang="fa" data-title="اهم" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Ohm_(unit%C3%A9)" title="Ohm (unité) – French" lang="fr" hreflang="fr" data-title="Ohm (unité)" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-fy mw-list-item"><a href="https://fy.wikipedia.org/wiki/Ohm_(ienheid)" title="Ohm (ienheid) – Western Frisian" lang="fy" hreflang="fy" data-title="Ohm (ienheid)" data-language-autonym="Frysk" data-language-local-name="Western Frisian" class="interlanguage-link-target"><span>Frysk</span></a></li><li class="interlanguage-link interwiki-ga mw-list-item"><a href="https://ga.wikipedia.org/wiki/%C3%93m" title="Óm – Irish" lang="ga" hreflang="ga" data-title="Óm" data-language-autonym="Gaeilge" data-language-local-name="Irish" class="interlanguage-link-target"><span>Gaeilge</span></a></li><li class="interlanguage-link interwiki-gv mw-list-item"><a href="https://gv.wikipedia.org/wiki/Ohm" title="Ohm – Manx" lang="gv" hreflang="gv" data-title="Ohm" data-language-autonym="Gaelg" data-language-local-name="Manx" class="interlanguage-link-target"><span>Gaelg</span></a></li><li class="interlanguage-link interwiki-gl mw-list-item"><a href="https://gl.wikipedia.org/wiki/Ohm" title="Ohm – Galician" lang="gl" hreflang="gl" data-title="Ohm" data-language-autonym="Galego" data-language-local-name="Galician" class="interlanguage-link-target"><span>Galego</span></a></li><li class="interlanguage-link interwiki-gan mw-list-item"><a href="https://gan.wikipedia.org/wiki/%E6%AD%90" title="歐 – Gan" lang="gan" hreflang="gan" data-title="歐" data-language-autonym="贛語" data-language-local-name="Gan" class="interlanguage-link-target"><span>贛語</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EC%98%B4_(%EB%8B%A8%EC%9C%84)" title="옴 (단위) – Korean" lang="ko" hreflang="ko" data-title="옴 (단위)" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D5%95%D5%B0%D5%B4_(%D5%B9%D5%A1%D6%83%D5%B4%D5%A1%D5%B6_%D5%B4%D5%AB%D5%A1%D5%BE%D5%B8%D6%80)" title="Օհմ (չափման միավոր) – Armenian" lang="hy" hreflang="hy" data-title="Օհմ (չափման միավոր)" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target"><span>Հայերեն</span></a></li><li class="interlanguage-link interwiki-hi mw-list-item"><a href="https://hi.wikipedia.org/wiki/%E0%A4%93%E0%A4%AE_(%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%8B%E0%A4%A7_%E0%A4%95%E0%A5%80_%E0%A4%87%E0%A4%95%E0%A4%BE%E0%A4%88)" title="ओम (प्रतिरोध की इकाई) – Hindi" lang="hi" hreflang="hi" data-title="ओम (प्रतिरोध की इकाई)" data-language-autonym="हिन्दी" data-language-local-name="Hindi" class="interlanguage-link-target"><span>हिन्दी</span></a></li><li class="interlanguage-link interwiki-hr mw-list-item"><a href="https://hr.wikipedia.org/wiki/Om" title="Om – Croatian" lang="hr" hreflang="hr" data-title="Om" data-language-autonym="Hrvatski" data-language-local-name="Croatian" class="interlanguage-link-target"><span>Hrvatski</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/Ohm" title="Ohm – Indonesian" lang="id" hreflang="id" data-title="Ohm" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-is mw-list-item"><a href="https://is.wikipedia.org/wiki/%C3%93m" title="Óm – Icelandic" lang="is" hreflang="is" data-title="Óm" data-language-autonym="Íslenska" data-language-local-name="Icelandic" class="interlanguage-link-target"><span>Íslenska</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Ohm" title="Ohm – Italian" lang="it" hreflang="it" data-title="Ohm" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/%D7%90%D7%95%D7%94%D7%9D" title="אוהם – Hebrew" lang="he" hreflang="he" data-title="אוהם" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-ka mw-list-item"><a href="https://ka.wikipedia.org/wiki/%E1%83%9D%E1%83%9B%E1%83%98_(%E1%83%94%E1%83%A0%E1%83%97%E1%83%94%E1%83%A3%E1%83%9A%E1%83%98)" title="ომი (ერთეული) – Georgian" lang="ka" hreflang="ka" data-title="ომი (ერთეული)" data-language-autonym="ქართული" data-language-local-name="Georgian" class="interlanguage-link-target"><span>ქართული</span></a></li><li class="interlanguage-link interwiki-kk mw-list-item"><a href="https://kk.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Kazakh" lang="kk" hreflang="kk" data-title="Ом" data-language-autonym="Қазақша" data-language-local-name="Kazakh" class="interlanguage-link-target"><span>Қазақша</span></a></li><li class="interlanguage-link interwiki-ht mw-list-item"><a href="https://ht.wikipedia.org/wiki/Ohm_(inite)" title="Ohm (inite) – Haitian Creole" lang="ht" hreflang="ht" data-title="Ohm (inite)" data-language-autonym="Kreyòl ayisyen" data-language-local-name="Haitian Creole" class="interlanguage-link-target"><span>Kreyòl ayisyen</span></a></li><li class="interlanguage-link interwiki-ky mw-list-item"><a href="https://ky.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Kyrgyz" lang="ky" hreflang="ky" data-title="Ом" data-language-autonym="Кыргызча" data-language-local-name="Kyrgyz" class="interlanguage-link-target"><span>Кыргызча</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Oms" title="Oms – Latvian" lang="lv" hreflang="lv" data-title="Oms" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Omas" title="Omas – Lithuanian" lang="lt" hreflang="lt" data-title="Omas" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target"><span>Lietuvių</span></a></li><li class="interlanguage-link interwiki-li mw-list-item"><a href="https://li.wikipedia.org/wiki/Ohm_(einheid)" title="Ohm (einheid) – Limburgish" lang="li" hreflang="li" data-title="Ohm (einheid)" data-language-autonym="Limburgs" data-language-local-name="Limburgish" class="interlanguage-link-target"><span>Limburgs</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/Ohm_(m%C3%A9rt%C3%A9kegys%C3%A9g)" title="Ohm (mértékegység) – Hungarian" lang="hu" hreflang="hu" data-title="Ohm (mértékegység)" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-mk mw-list-item"><a href="https://mk.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Macedonian" lang="mk" hreflang="mk" data-title="Ом" data-language-autonym="Македонски" data-language-local-name="Macedonian" class="interlanguage-link-target"><span>Македонски</span></a></li><li class="interlanguage-link interwiki-ml mw-list-item"><a href="https://ml.wikipedia.org/wiki/%E0%B4%93%E0%B4%82_(%E0%B4%AF%E0%B5%82%E0%B4%A3%E0%B4%BF%E0%B4%B1%E0%B5%8D%E0%B4%B1%E0%B5%8D)" title="ഓം (യൂണിറ്റ്) – Malayalam" lang="ml" hreflang="ml" data-title="ഓം (യൂണിറ്റ്)" data-language-autonym="മലയാളം" data-language-local-name="Malayalam" class="interlanguage-link-target"><span>മലയാളം</span></a></li><li class="interlanguage-link interwiki-mr mw-list-item"><a href="https://mr.wikipedia.org/wiki/%E0%A4%93%E0%A4%B9%E0%A5%8D%E0%A4%AE" title="ओह्म – Marathi" lang="mr" hreflang="mr" data-title="ओह्म" data-language-autonym="मराठी" data-language-local-name="Marathi" class="interlanguage-link-target"><span>मराठी</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Ohm" title="Ohm – Malay" lang="ms" hreflang="ms" data-title="Ohm" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-mn mw-list-item"><a href="https://mn.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Mongolian" lang="mn" hreflang="mn" data-title="Ом" data-language-autonym="Монгол" data-language-local-name="Mongolian" class="interlanguage-link-target"><span>Монгол</span></a></li><li class="interlanguage-link interwiki-my mw-list-item"><a href="https://my.wikipedia.org/wiki/%E1%80%A1%E1%80%AF%E1%80%99%E1%80%BA%E1%80%B8" title="အုမ်း – Burmese" lang="my" hreflang="my" data-title="အုမ်း" data-language-autonym="မြန်မာဘာသာ" data-language-local-name="Burmese" class="interlanguage-link-target"><span>မြန်မာဘာသာ</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Ohm_(eenheid)" title="Ohm (eenheid) – Dutch" lang="nl" hreflang="nl" data-title="Ohm (eenheid)" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E3%82%AA%E3%83%BC%E3%83%A0" title="オーム – Japanese" lang="ja" hreflang="ja" data-title="オーム" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-frr badge-Q70894304 mw-list-item" title=""><a href="https://frr.wikipedia.org/wiki/Ohm_(ianhaid)" title="Ohm (ianhaid) – Northern Frisian" lang="frr" hreflang="frr" data-title="Ohm (ianhaid)" data-language-autonym="Nordfriisk" data-language-local-name="Northern Frisian" class="interlanguage-link-target"><span>Nordfriisk</span></a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Ohm" title="Ohm – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Ohm" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target"><span>Norsk bokmål</span></a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/Ohm" title="Ohm – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Ohm" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-oc mw-list-item"><a href="https://oc.wikipedia.org/wiki/Ohm" title="Ohm – Occitan" lang="oc" hreflang="oc" data-title="Ohm" data-language-autonym="Occitan" data-language-local-name="Occitan" class="interlanguage-link-target"><span>Occitan</span></a></li><li class="interlanguage-link interwiki-uz mw-list-item"><a href="https://uz.wikipedia.org/wiki/Om" title="Om – Uzbek" lang="uz" hreflang="uz" data-title="Om" data-language-autonym="Oʻzbekcha / ўзбекча" data-language-local-name="Uzbek" class="interlanguage-link-target"><span>Oʻzbekcha / ўзбекча</span></a></li><li class="interlanguage-link interwiki-pa mw-list-item"><a href="https://pa.wikipedia.org/wiki/%E0%A8%93%E0%A8%B9%E0%A8%AE" title="ਓਹਮ – Punjabi" lang="pa" hreflang="pa" data-title="ਓਹਮ" data-language-autonym="ਪੰਜਾਬੀ" data-language-local-name="Punjabi" class="interlanguage-link-target"><span>ਪੰਜਾਬੀ</span></a></li><li class="interlanguage-link interwiki-pnb mw-list-item"><a href="https://pnb.wikipedia.org/wiki/%D8%A7%D9%88%DB%81%D9%85" title="اوہم – Western Punjabi" lang="pnb" hreflang="pnb" data-title="اوہم" data-language-autonym="پنجابی" data-language-local-name="Western Punjabi" class="interlanguage-link-target"><span>پنجابی</span></a></li><li class="interlanguage-link interwiki-jam mw-list-item"><a href="https://jam.wikipedia.org/wiki/Uom" title="Uom – Jamaican Creole English" lang="jam" hreflang="jam" data-title="Uom" data-language-autonym="Patois" data-language-local-name="Jamaican Creole English" class="interlanguage-link-target"><span>Patois</span></a></li><li class="interlanguage-link interwiki-pms mw-list-item"><a href="https://pms.wikipedia.org/wiki/Ohm" title="Ohm – Piedmontese" lang="pms" hreflang="pms" data-title="Ohm" data-language-autonym="Piemontèis" data-language-local-name="Piedmontese" class="interlanguage-link-target"><span>Piemontèis</span></a></li><li class="interlanguage-link interwiki-nds mw-list-item"><a href="https://nds.wikipedia.org/wiki/Ohm_(Eenheit)" title="Ohm (Eenheit) – Low German" lang="nds" hreflang="nds" data-title="Ohm (Eenheit)" data-language-autonym="Plattdüütsch" data-language-local-name="Low German" class="interlanguage-link-target"><span>Plattdüütsch</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Om_(jednostka)" title="Om (jednostka) – Polish" lang="pl" hreflang="pl" data-title="Om (jednostka)" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Ohm" title="Ohm – Portuguese" lang="pt" hreflang="pt" data-title="Ohm" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Ohm" title="Ohm – Romanian" lang="ro" hreflang="ro" data-title="Ohm" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Russian" lang="ru" hreflang="ru" data-title="Ом" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sq mw-list-item"><a href="https://sq.wikipedia.org/wiki/Ohm" title="Ohm – Albanian" lang="sq" hreflang="sq" data-title="Ohm" data-language-autonym="Shqip" data-language-local-name="Albanian" class="interlanguage-link-target"><span>Shqip</span></a></li><li class="interlanguage-link interwiki-scn mw-list-item"><a href="https://scn.wikipedia.org/wiki/Ohm" title="Ohm – Sicilian" lang="scn" hreflang="scn" data-title="Ohm" data-language-autonym="Sicilianu" data-language-local-name="Sicilian" class="interlanguage-link-target"><span>Sicilianu</span></a></li><li class="interlanguage-link interwiki-si mw-list-item"><a href="https://si.wikipedia.org/wiki/%E0%B6%95%E0%B6%B8%E0%B7%8A" title="ඕම් – Sinhala" lang="si" hreflang="si" data-title="ඕම්" data-language-autonym="සිංහල" data-language-local-name="Sinhala" class="interlanguage-link-target"><span>සිංහල</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Ohm" title="Ohm – Simple English" lang="en-simple" hreflang="en-simple" data-title="Ohm" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/Ohm_(jednotka)" title="Ohm (jednotka) – Slovak" lang="sk" hreflang="sk" data-title="Ohm (jednotka)" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-sl mw-list-item"><a href="https://sl.wikipedia.org/wiki/Om" title="Om – Slovenian" lang="sl" hreflang="sl" data-title="Om" data-language-autonym="Slovenščina" data-language-local-name="Slovenian" class="interlanguage-link-target"><span>Slovenščina</span></a></li><li class="interlanguage-link interwiki-ckb mw-list-item"><a href="https://ckb.wikipedia.org/wiki/%D8%A6%DB%86%D9%85" title="ئۆم – Central Kurdish" lang="ckb" hreflang="ckb" data-title="ئۆم" data-language-autonym="کوردی" data-language-local-name="Central Kurdish" class="interlanguage-link-target"><span>کوردی</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/%D0%9E%D0%BC_(%D1%98%D0%B5%D0%B4%D0%B8%D0%BD%D0%B8%D1%86%D0%B0)" title="Ом (јединица) – Serbian" lang="sr" hreflang="sr" data-title="Ом (јединица)" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-sh mw-list-item"><a href="https://sh.wikipedia.org/wiki/Om_(jedinica)" title="Om (jedinica) – Serbo-Croatian" lang="sh" hreflang="sh" data-title="Om (jedinica)" data-language-autonym="Srpskohrvatski / српскохрватски" data-language-local-name="Serbo-Croatian" class="interlanguage-link-target"><span>Srpskohrvatski / српскохрватски</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/Ohmi" title="Ohmi – Finnish" lang="fi" hreflang="fi" data-title="Ohmi" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Ohm" title="Ohm – Swedish" lang="sv" hreflang="sv" data-title="Ohm" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%93%E0%AE%AE%E0%AF%8D_(%E0%AE%AE%E0%AE%BF%E0%AE%A9%E0%AF%8D%E0%AE%A9%E0%AE%BF%E0%AE%AF%E0%AE%B2%E0%AF%8D)" title="ஓம் (மின்னியல்) – Tamil" lang="ta" hreflang="ta" data-title="ஓம் (மின்னியல்)" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target"><span>தமிழ்</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/%E0%B9%82%E0%B8%AD%E0%B8%AB%E0%B9%8C%E0%B8%A1" title="โอห์ม – Thai" lang="th" hreflang="th" data-title="โอห์ม" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Ohm" title="Ohm – Turkish" lang="tr" hreflang="tr" data-title="Ohm" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%9E%D0%BC" title="Ом – Ukrainian" lang="uk" hreflang="uk" data-title="Ом" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-ur mw-list-item"><a href="https://ur.wikipedia.org/wiki/%D8%A7%D9%88%DB%81%D9%85" title="اوہم – Urdu" lang="ur" hreflang="ur" data-title="اوہم" data-language-autonym="اردو" data-language-local-name="Urdu" class="interlanguage-link-target"><span>اردو</span></a></li><li class="interlanguage-link interwiki-vi mw-list-item"><a href="https://vi.wikipedia.org/wiki/Ohm" title="Ohm – Vietnamese" lang="vi" hreflang="vi" data-title="Ohm" data-language-autonym="Tiếng Việt" data-language-local-name="Vietnamese" class="interlanguage-link-target"><span>Tiếng Việt</span></a></li><li class="interlanguage-link interwiki-war mw-list-item"><a href="https://war.wikipedia.org/wiki/Ohm" title="Ohm – Waray" lang="war" hreflang="war" data-title="Ohm" data-language-autonym="Winaray" data-language-local-name="Waray" class="interlanguage-link-target"><span>Winaray</span></a></li><li class="interlanguage-link interwiki-wuu mw-list-item"><a href="https://wuu.wikipedia.org/wiki/%E6%AC%A7%E5%A7%86" title="欧姆 – Wu" lang="wuu" hreflang="wuu" data-title="欧姆" data-language-autonym="吴语" data-language-local-name="Wu" class="interlanguage-link-target"><span>吴语</span></a></li><li class="interlanguage-link interwiki-zh-yue mw-list-item"><a href="https://zh-yue.wikipedia.org/wiki/%E6%AD%90%E5%A7%86" title="歐姆 – Cantonese" lang="yue" hreflang="yue" data-title="歐姆" data-language-autonym="粵語" data-language-local-name="Cantonese" class="interlanguage-link-target"><span>粵語</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E6%AD%90%E5%A7%86" title="歐姆 – Chinese" lang="zh" hreflang="zh" data-title="歐姆" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q47083#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-nstab-main" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Ohm" title="View the content page [c]" accesskey="c"><span>Article</span></a></li><li id="ca-talk" class="vector-tab-noicon mw-list-item"><a href="/wiki/Talk:Ohm" 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nomobile noexcerpt noprint searchaux" style="display:none">SI derived unit of electrical resistance</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">This article is about the SI derived unit. For other uses, see <a href="/wiki/Ohm_(disambiguation)" class="mw-disambig" title="Ohm (disambiguation)">Ohm (disambiguation)</a>.</div> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox ib-unit"><tbody><tr><th colspan="2" class="infobox-above">ohm</th></tr><tr><td colspan="2" class="infobox-image"><span typeof="mw:File"><a href="/wiki/File:Leeds_and_Northrup_one_ohm_standard_resistance.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/ef/Leeds_and_Northrup_one_ohm_standard_resistance.jpg/250px-Leeds_and_Northrup_one_ohm_standard_resistance.jpg" decoding="async" width="240" height="226" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/ef/Leeds_and_Northrup_one_ohm_standard_resistance.jpg/360px-Leeds_and_Northrup_one_ohm_standard_resistance.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/e/ef/Leeds_and_Northrup_one_ohm_standard_resistance.jpg 2x" data-file-width="424" data-file-height="400" /></a></span><div class="infobox-caption">A laboratory one-ohm standard resistor, <abbr title="circa">c.</abbr><span style="white-space:nowrap;"> 1917</span></div></td></tr><tr><th colspan="2" class="infobox-header">General information</th></tr><tr><th scope="row" class="infobox-label"><a href="/wiki/System_of_units_of_measurement" title="System of units of measurement">Unit system</a></th><td class="infobox-data"><a href="/wiki/SI" class="mw-redirect" title="SI">SI</a></td></tr><tr><th scope="row" class="infobox-label">Unit of</th><td class="infobox-data"><a href="/wiki/Electrical_resistance" class="mw-redirect" title="Electrical resistance">electrical resistance</a></td></tr><tr><th scope="row" class="infobox-label">Symbol</th><td class="infobox-data">Ω</td></tr><tr><th scope="row" class="infobox-label">Named after</th><td class="infobox-data"><a href="/wiki/Georg_Ohm" title="Georg Ohm">Georg Ohm</a></td></tr><tr><th colspan="2" class="infobox-header">Conversions </th></tr><tr class="nowrap"><td>1 Ω <i>in ...</i></td><td><i>... is equal to ...</i></td></tr><tr style="display:none"><th colspan="2"> </th></tr><tr><th scope="row" class="infobox-label"><span class="nowrap">   </span><a href="/wiki/SI_base_unit" title="SI base unit">SI base units</a></th><td class="infobox-data"><span class="nowrap">   </span><a href="/wiki/Kilogram" title="Kilogram">kg</a>⋅<a href="/wiki/Metre" title="Metre">m</a><sup>2</sup>⋅<a href="/wiki/Second" title="Second">s</a><sup>−3</sup>⋅<a href="/wiki/Ampere" title="Ampere">A</a><sup>−2</sup></td></tr></tbody></table><style data-mw-deduplicate="TemplateStyles:r1236303919">@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-has-images-with-white-backgrounds img{background:white}}</style> <p>The <b>ohm</b> (symbol: <b>Ω</b>, the uppercase Greek letter <a href="/wiki/Omega" title="Omega">omega</a>) is the unit of <a href="/wiki/Electrical_resistance" class="mw-redirect" title="Electrical resistance">electrical resistance</a> in the <a href="/wiki/International_System_of_Units" title="International System of Units">International System of Units (SI)</a>. It is named after German physicist <a href="/wiki/Georg_Ohm" title="Georg Ohm">Georg Ohm</a> (1789–1854). Various empirically derived standard units for electrical resistance were developed in connection with early <a href="/wiki/Telegraphy" title="Telegraphy">telegraphy</a> practice, and the <a href="/wiki/British_Association_for_the_Advancement_of_Science" class="mw-redirect" title="British Association for the Advancement of Science">British Association for the Advancement of Science</a> proposed a unit derived from existing units of mass, length and time, and of a convenient scale for practical work as early as 1861. </p><p>Following the <a href="/wiki/2019_revision_of_the_SI" title="2019 revision of the SI">2019 revision of the SI</a>, in which the <a href="/wiki/Ampere" title="Ampere">ampere</a> and the <a href="/wiki/Kilogram" title="Kilogram">kilogram</a> were redefined in terms of fundamental constants, the ohm is now also defined as an exact value in terms of these constants. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Definition">Definition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=1" title="Edit section: Definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Electronic_multi_meter.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/24/Electronic_multi_meter.jpg/250px-Electronic_multi_meter.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/24/Electronic_multi_meter.jpg/330px-Electronic_multi_meter.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/24/Electronic_multi_meter.jpg/500px-Electronic_multi_meter.jpg 2x" data-file-width="1600" data-file-height="1067" /></a><figcaption>One of the functions of many types of <a href="/wiki/Multimeter" title="Multimeter">multimeters</a> is the measurement of resistance in ohms.</figcaption></figure> <p>The ohm is defined as an electrical resistance between two points of a conductor when a constant potential difference of one <a href="/wiki/Volt" title="Volt">volt</a> (V), applied to these points, produces in the conductor a current of one <a href="/wiki/Ampere" title="Ampere">ampere</a> (A), the conductor not being the seat of any <a href="/wiki/Electromotive_force" title="Electromotive force">electromotive force</a>.<sup id="cite_ref-BIPM_SI9_1-0" class="reference"><a href="#cite_note-BIPM_SI9-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \Omega ={\dfrac {\text{V}}{\text{A}}}={\dfrac {1}{\text{S}}}={\dfrac {\text{W}}{{\text{A}}^{2}}}={\dfrac {{\text{V}}^{2}}{\text{W}}}={\dfrac {\text{s}}{\text{F}}}={\dfrac {\text{H}}{\text{s}}}={\dfrac {\text{Wb}}{\text{C}}}={\dfrac {{\text{J}}{\cdot }{\text{s}}}{{\text{C}}^{2}}}={\dfrac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}{\cdot }{\text{C}}^{2}}}={\dfrac {\text{J}}{{\text{s}}{\cdot }{\text{A}}^{2}}}={\dfrac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}^{3}{\cdot }{\text{A}}^{2}}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi mathvariant="normal">Ω</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mtext>V</mtext> <mtext>A</mtext> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mn>1</mn> <mtext>S</mtext> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mtext>W</mtext> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>V</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mtext>W</mtext> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mtext>s</mtext> <mtext>F</mtext> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mtext>H</mtext> <mtext>s</mtext> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mtext>Wb</mtext> <mtext>C</mtext> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>J</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>⋅</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>s</mtext> </mrow> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>C</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>kg</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>⋅</mo> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>m</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>s</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>⋅</mo> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>C</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mtext>J</mtext> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>s</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>⋅</mo> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> </mfrac> </mstyle> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mfrac> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>kg</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>⋅</mo> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>m</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> <mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>s</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>3</mn> </mrow> </msup> <mrow class="MJX-TeXAtom-ORD"> <mo>⋅</mo> </mrow> <msup> <mrow class="MJX-TeXAtom-ORD"> <mtext>A</mtext> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> </mrow> </mfrac> </mstyle> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \Omega ={\dfrac {\text{V}}{\text{A}}}={\dfrac {1}{\text{S}}}={\dfrac {\text{W}}{{\text{A}}^{2}}}={\dfrac {{\text{V}}^{2}}{\text{W}}}={\dfrac {\text{s}}{\text{F}}}={\dfrac {\text{H}}{\text{s}}}={\dfrac {\text{Wb}}{\text{C}}}={\dfrac {{\text{J}}{\cdot }{\text{s}}}{{\text{C}}^{2}}}={\dfrac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}{\cdot }{\text{C}}^{2}}}={\dfrac {\text{J}}{{\text{s}}{\cdot }{\text{A}}^{2}}}={\dfrac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}^{3}{\cdot }{\text{A}}^{2}}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/13fe562a0c1dc84b1ac1d5b630517bf0624ddc3f" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.505ex; width:79.703ex; height:6.343ex;" alt="{\displaystyle \Omega ={\dfrac {\text{V}}{\text{A}}}={\dfrac {1}{\text{S}}}={\dfrac {\text{W}}{{\text{A}}^{2}}}={\dfrac {{\text{V}}^{2}}{\text{W}}}={\dfrac {\text{s}}{\text{F}}}={\dfrac {\text{H}}{\text{s}}}={\dfrac {\text{Wb}}{\text{C}}}={\dfrac {{\text{J}}{\cdot }{\text{s}}}{{\text{C}}^{2}}}={\dfrac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}{\cdot }{\text{C}}^{2}}}={\dfrac {\text{J}}{{\text{s}}{\cdot }{\text{A}}^{2}}}={\dfrac {{\text{kg}}{\cdot }{\text{m}}^{2}}{{\text{s}}^{3}{\cdot }{\text{A}}^{2}}}}" /></span></dd></dl> <p>In which the following additional units appear: <a href="/wiki/Siemens_(unit)" title="Siemens (unit)">siemens</a> (S), <a href="/wiki/Watt" title="Watt">watt</a> (W), <a href="/wiki/Second" title="Second">second</a> (s), <a href="/wiki/Farad" title="Farad">farad</a> (F), <a href="/wiki/Henry_(unit)" title="Henry (unit)">henry</a> (H), <a href="/wiki/Weber_(unit)" title="Weber (unit)">weber</a> (Wb), <a href="/wiki/Joule" title="Joule">joule</a> (J), <a href="/wiki/Coulomb" title="Coulomb">coulomb</a> (C), <a href="/wiki/Kilogram" title="Kilogram">kilogram</a> (kg), and <a href="/wiki/Metre" title="Metre">meter</a> (m). </p><p>In many cases the resistance of a conductor is approximately constant within a certain range of voltages, temperatures, and other parameters. These are called <a href="/wiki/Linear" class="mw-redirect" title="Linear">linear</a> <a href="/wiki/Resistor" title="Resistor">resistors</a>. In other cases resistance varies, such as in the case of the <a href="/wiki/Thermistor" title="Thermistor">thermistor</a>, which exhibits a strong dependence of its resistance with temperature. </p><p>In the US, a double vowel in the prefixed units "kiloohm" and "megaohm" is commonly simplified, producing "kilohm" and "megohm".<sup id="cite_ref-SI10-2002_2-0" class="reference"><a href="#cite_note-SI10-2002-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Thompson-Taylor_2008_3-0" class="reference"><a href="#cite_note-Thompson-Taylor_2008-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-NIST_2016_4-0" class="reference"><a href="#cite_note-NIST_2016-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Aubrecht-French-Iona_2012_5-0" class="reference"><a href="#cite_note-Aubrecht-French-Iona_2012-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p><p>In alternating current circuits, <a href="/wiki/Electrical_impedance" title="Electrical impedance">electrical impedance</a> is also measured in ohms. </p> <div class="mw-heading mw-heading2"><h2 id="Relation_to_conductance">Relation to conductance</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=2" title="Edit section: Relation to conductance"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <a href="/wiki/Siemens_(unit)" title="Siemens (unit)">siemens</a> (S) is the <a href="/wiki/SI_derived_unit" title="SI derived unit">SI derived unit</a> of <a href="/wiki/Electric_conductance" class="mw-redirect" title="Electric conductance">electric conductance</a> and <a href="/wiki/Admittance" title="Admittance">admittance</a>, historically known as the "mho" (<i>ohm</i> spelled backwards, symbol is ℧); it is one <a href="/wiki/Multiplicative_inverse" title="Multiplicative inverse">reciprocal</a> ohm: <span class="nowrap">1 S = 1 Ω<sup>−1</sup>.</span> </p> <div class="mw-heading mw-heading2"><h2 id="Power_as_a_function_of_resistance">Power as a function of resistance</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=3" title="Edit section: Power as a function of resistance"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The power dissipated by a <a href="/wiki/Resistor" title="Resistor">resistor</a> may be calculated from its resistance, and the voltage or current involved. The formula is a combination of <a href="/wiki/Ohm%27s_law" title="Ohm's law">Ohm's law</a> and <a href="/wiki/Joule%27s_first_law" class="mw-redirect" title="Joule's first law">Joule's law</a>: <span class="mwe-math-element"><span class="mwe-math-mathml-display mwe-math-mathml-a11y" style="display: none;"><math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle P=VI={\frac {V^{2}}{R}}=I^{2}R,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>P</mi> <mo>=</mo> <mi>V</mi> <mi>I</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msup> <mi>V</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mi>R</mi> </mfrac> </mrow> <mo>=</mo> <msup> <mi>I</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>2</mn> </mrow> </msup> <mi>R</mi> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle P=VI={\frac {V^{2}}{R}}=I^{2}R,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4a055fe9f59549765e2773064ed1b1adbe977bd0" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.005ex; width:22.489ex; height:5.843ex;" alt="{\displaystyle P=VI={\frac {V^{2}}{R}}=I^{2}R,}" /></span> </p><p>where <span class="texhtml mvar" style="font-style:italic;">P</span> is the power, <span class="texhtml mvar" style="font-style:italic;">R</span> is the resistance, <span class="texhtml mvar" style="font-style:italic;">V</span> is the <a href="/wiki/Voltage" title="Voltage">voltage</a> across the resistor, and <span class="texhtml mvar" style="font-style:italic;">I</span> is the current through the resistor. </p><p>A linear resistor has a constant resistance value over all applied voltages or currents; many practical resistors are linear over a useful range of currents. Non-linear resistors have a value that may vary depending on the applied voltage (or current). Where <a href="/wiki/Alternating_current" title="Alternating current">alternating current</a> is applied to the circuit (or where the resistance value is a function of time), the relation above is true at any instant, but calculation of average power over an interval of time requires <a href="/wiki/Integral" title="Integral">integration</a> of "instantaneous" power over that interval. </p><p>Since the ohm belongs to a <a href="/wiki/Coherence_(units_of_measurement)" title="Coherence (units of measurement)">coherent system of units</a>, when each of these quantities has its corresponding SI unit (<a href="/wiki/Watt" title="Watt">watt</a> for <span class="texhtml mvar" style="font-style:italic;">P</span>, ohm for <span class="texhtml mvar" style="font-style:italic;">R</span>, <a href="/wiki/Volt" title="Volt">volt</a> for <span class="texhtml mvar" style="font-style:italic;">V</span> and <a href="/wiki/Ampere" title="Ampere">ampere</a> for <span class="texhtml mvar" style="font-style:italic;">I</span>, which are related as in <a href="#Definition">§ Definition</a>) this formula remains valid numerically when these units are used (and thought of as being cancelled or omitted). </p> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=4" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The rapid rise of electrotechnology in the last half of the 19th century created a demand for a rational, coherent, consistent, and international system of units for electrical quantities. Telegraphers and other early users of electricity in the 19th century needed a practical standard unit of measurement for resistance. Resistance was often expressed as a multiple of the resistance of a standard length of telegraph wires; different agencies used different bases for a standard, so units were not readily interchangeable. Electrical units so defined were not a coherent system with the units for energy, mass, length, and time, requiring conversion factors to be used in calculations relating energy or power to resistance.<sup id="cite_ref-Hunt_1994_6-0" class="reference"><a href="#cite_note-Hunt_1994-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p><p>Two different methods of establishing a system of electrical units can be chosen. Various artifacts, such as a length of wire or a standard <a href="/wiki/Electrochemical" class="mw-redirect" title="Electrochemical">electrochemical</a> cell, could be specified as producing defined quantities for resistance, voltage, and so on. Alternatively, the electrical units can be related to the mechanical units by defining, for example, a unit of current that gives a specified force between two wires, or a unit of charge that gives a unit of force between two unit charges. This latter method ensures coherence with the units of energy. Defining a unit for resistance that is coherent with units of energy and time in effect also requires defining units for potential and current. It is desirable that one unit of electrical potential will force one unit of electric current through one unit of electrical resistance, doing one unit of work in one unit of time, otherwise, all electrical calculations will require conversion factors. </p><p>Since so-called "absolute" units of charge and current are expressed as combinations of units of mass, length, and time, <a href="/wiki/Dimensional_analysis" title="Dimensional analysis">dimensional analysis</a> of the relations between potential, current, and resistance show that resistance is expressed in units of length per time – a velocity. Some early definitions of a unit of resistance, for example, defined a unit resistance as one quadrant of the Earth per second. </p><p>The absolute-unit system related magnetic and electrostatic quantities to metric base units of mass, time, and length. These units had the great advantage of simplifying the equations used in the solution of electromagnetic problems, and eliminated conversion factors in calculations about electrical quantities. However, the centimeter–gram–second, CGS, units turned out to have impractical sizes for practical measurements. </p><p>Various artifact standards were proposed as the definition of the unit of resistance. In 1860 <a href="/wiki/Werner_Siemens" class="mw-redirect" title="Werner Siemens">Werner Siemens</a> (1816–1892) published a suggestion for a reproducible resistance standard in <a href="/wiki/Johann_Christian_Poggendorff" title="Johann Christian Poggendorff">Poggendorff's</a> <i><a href="/wiki/Annalen_der_Physik_und_Chemie" class="mw-redirect" title="Annalen der Physik und Chemie">Annalen der Physik und Chemie</a></i>.<sup id="cite_ref-Siemens_1860_7-0" class="reference"><a href="#cite_note-Siemens_1860-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> He proposed a column of pure mercury, of one square millimeter cross section, one meter long: <a href="/wiki/Siemens_mercury_unit" title="Siemens mercury unit">Siemens mercury unit</a>. However, this unit was not coherent with other units. One proposal was to devise a unit based on a mercury column that would be coherent – in effect, adjusting the length to make the resistance one ohm. Not all users of units had the resources to carry out <a href="/wiki/Metrology" title="Metrology">metrology</a> experiments to the required precision, so working standards notionally based on the physical definition were required. </p><p>In 1861, <a href="/wiki/Josiah_Latimer_Clark" title="Josiah Latimer Clark">Latimer Clark</a> (1822–1898) and <a href="/wiki/Charles_Tilston_Bright" title="Charles Tilston Bright">Sir Charles Bright</a> (1832–1888) presented a paper at the <a href="/wiki/British_Association_for_the_Advancement_of_Science" class="mw-redirect" title="British Association for the Advancement of Science">British Association for the Advancement of Science</a> meeting <sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> suggesting that standards for electrical units be established and suggesting names for these units derived from eminent philosophers, 'Ohma', 'Farad' and 'Volt'. The <a href="/wiki/British_Association_for_the_Advancement_of_Science" class="mw-redirect" title="British Association for the Advancement of Science">BAAS</a> in 1861 appointed a committee including <a href="/wiki/James_Clerk_Maxwell" title="James Clerk Maxwell">Maxwell</a> and <a href="/wiki/William_Thomson,_1st_Baron_Kelvin" class="mw-redirect" title="William Thomson, 1st Baron Kelvin">Thomson</a> to report upon standards of electrical resistance.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> Their objectives were to devise a unit that was of convenient size, part of a complete system for electrical measurements, coherent with the units for energy, stable, reproducible and based on the French metrical system.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> In the third report of the committee, 1864, the resistance unit is referred to as "B.A. unit, or Ohmad".<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> By 1867 the unit is referred to as simply <i>ohm</i>.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> </p><p>The B.A. ohm was intended to be 10<sup>9</sup> CGS units but owing to an error in calculations the definition was 1.3% too small. The error was significant for preparation of working standards. </p><p>On 21 September 1881 the <a href="/wiki/International_Electrical_Congress" title="International Electrical Congress">International Electrical Congress</a> defined a <i>practical</i> unit of ohm for the resistance, based on <a href="/wiki/CGS" class="mw-redirect" title="CGS">CGS</a> units, using a mercury column 1 mm<sup>2</sup> in cross-section, approximately 104.9 cm in length at 0 °C, similar to the apparatus suggested by Siemens. </p><p>A <i>legal</i> ohm, a reproducible standard, was defined by the international conference of electricians at Paris in 1884 as the resistance of a mercury column of specified weight and 106 cm long; this was a compromise value between the B. A. unit (equivalent to 104.7 cm), the Siemens unit (100 cm by definition), and the CGS unit.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> Although called "legal", this standard was not adopted by any national legislation. The "international" ohm was recommended by unanimous resolution at the International Electrical Congress 1893 in Chicago.<sup id="cite_ref-eb11-p742_14-0" class="reference"><a href="#cite_note-eb11-p742-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> The unit was based upon the ohm equal to 10<sup>9</sup> units of resistance of the C.G.S. system of electromagnetic units. The international ohm is represented by the resistance offered to an unvarying electric current in a mercury column of constant cross-sectional area 106.3 cm long of mass 14.4521 grams and 0 °C. This definition became the basis for the legal definition of the ohm in several countries. In 1908, this definition was adopted by scientific representatives from several countries at the International Conference on Electric Units and Standards in London.<sup id="cite_ref-eb11-p742_14-1" class="reference"><a href="#cite_note-eb11-p742-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> The mercury column standard was maintained until the 1948 <a href="/wiki/General_Conference_on_Weights_and_Measures" title="General Conference on Weights and Measures">General Conference on Weights and Measures</a>, at which the ohm was redefined in absolute terms instead of as an artifact standard. </p><p>By the end of the 19th century, units were well understood and consistent. Definitions would change with little effect on commercial uses of the units. Advances in metrology allowed definitions to be formulated with a high degree of precision and repeatability. </p> <div class="mw-heading mw-heading3"><h3 id="Historical_units_of_resistance">Historical units of resistance</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=5" title="Edit section: Historical units of resistance"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable"> <tbody><tr> <th align="left">Unit<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </th> <th align="left">Definition </th> <th align="left">Value in B.A. ohms </th> <th align="left">Remarks </th></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>Absolute foot/second × 10<sup>7</sup> </td> <td>using imperial units </td> <td>0.3048 </td> <td>considered obsolete even in 1884 </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>Thomson's unit </td> <td>using imperial units </td> <td>0.3202 </td> <td>100 million ft/s (30,480 km/s), considered obsolete even in 1884 </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>Jacobi copper unit </td> <td>A specified copper wire 25 ft (7.620 m) long weighing 345 gr (22.36 g) </td> <td>0.6367 </td> <td>Used in 1850s </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>Weber's absolute unit × 10<sup>7</sup> </td> <td>Based on the meter and the second </td> <td>0.9191 </td> <td> </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td><a href="/wiki/Siemens_mercury_unit" title="Siemens mercury unit">Siemens mercury unit</a> </td> <td>1860. A column of pure mercury </td> <td>0.9537 </td> <td>100 cm and 1 mm<sup>2</sup> cross section at 0 °C </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td><a href="/wiki/British_Science_Association#Electrical_standards" title="British Science Association">British Association (B.A.) "ohm"</a> </td> <td>1863 </td> <td>1.000 </td> <td>Standard coils deposited at Kew Observatory in 1863<sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>Digney, Breguet, Swiss </td> <td> </td> <td>9.266–10.420 </td> <td>Iron wire 1 km long and 4 mm<sup>2</sup> cross section </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>Matthiessen </td> <td> </td> <td>13.59 </td> <td>1 mi (1.609 km) of <style data-mw-deduplicate="TemplateStyles:r1154941027">.mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="frac"><span class="num">1</span>⁄<span class="den">16</span></span>-inch-diameter (1.588 mm) pure annealed copper wire at 15.5 °C </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>Varley </td> <td> </td> <td>25.61 </td> <td>One mile of special <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027" /><span class="frac"><span class="num">1</span>⁄<span class="den">16</span></span>-inch-diameter copper wire </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td>German mile </td> <td> </td> <td>57.44 </td> <td>A German mile (8,238 yd or 7,533 m) of iron wire <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027" /><span class="frac"><span class="num">1</span>⁄<span class="den">6</span></span> in (4.233 mm) diameter </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td><a href="/wiki/Abohm" title="Abohm">Abohm</a> </td> <td> </td> <td>10<sup>−9</sup> </td> <td>Electromagnetic absolute unit in centimeter–gram–second units </td></tr> <tr style="vertical-align:top; border-bottom:1px solid #999;"> <td><a href="/wiki/Statohm" title="Statohm">Statohm</a> </td> <td> </td> <td><span class="nowrap"><span data-sort-value="7011898755178699999♠"></span>8.987<span style="margin-left:.25em;">551</span><span style="margin-left:.25em;">787</span><span style="margin-left:0.25em;margin-right:0.15em;">×</span>10<sup>11</sup></span> </td> <td>Electrostatic absolute unit in centimeter–gram–second units </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="Realization_of_standards">Realization of standards</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=6" title="Edit section: Realization of standards"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The mercury column method of realizing a physical standard ohm turned out to be difficult to reproduce, owing to the effects of non-constant cross section of the glass tubing. Various resistance coils were constructed by the British Association and others, to serve as physical artifact standards for the unit of resistance. The long-term stability and reproducibility of these artifacts was an ongoing field of research, as the effects of temperature, air pressure, humidity, and time on the standards were detected and analyzed. </p><p>Artifact standards are still used, but <a href="/wiki/Metrology" title="Metrology">metrology</a> experiments relating accurately dimensioned inductors and capacitors provided a more fundamental basis for the definition of the ohm. Since 1990 the <a href="/wiki/Quantum_Hall_effect" title="Quantum Hall effect">quantum Hall effect</a> has been used to define the ohm with high precision and repeatability. The quantum Hall experiments are used to check the stability of working standards that have convenient values for comparison.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> </p><p>Following the <a href="/wiki/2019_revision_of_the_SI" title="2019 revision of the SI">2019 revision of the SI</a>, in which the <a href="/wiki/Ampere" title="Ampere">ampere</a> and the <a href="/wiki/Kilogram" title="Kilogram">kilogram</a> were redefined in terms of <a href="/wiki/Physical_constant" title="Physical constant">fundamental constants</a>, the ohm is now also defined in terms of these constants. </p> <div class="mw-heading mw-heading2"><h2 id="Symbol">Symbol</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=7" title="Edit section: Symbol"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The symbol Ω was suggested, because of the similar sound of ohm and omega, by <a href="/wiki/William_Henry_Preece" title="William Henry Preece">William Henry Preece</a> in 1867.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> In documents printed before Second World War the unit symbol often consisted of the raised lowercase omega (ω), such that 56 Ω was written as 56<sup>ω</sup>. </p><p>Historically, some document editing software applications have used the <a href="/wiki/Symbol_(typeface)" title="Symbol (typeface)">Symbol typeface</a> to render the character Ω.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> Where the font is not supported, the same document may be displayed with a "W" ("10 W" instead of "10 Ω", for instance). As W represents the <a href="/wiki/Watt" title="Watt">watt</a>, the SI unit of <a href="/wiki/Power_(physics)" title="Power (physics)">power</a>, this can lead to confusion, making the use of the correct Unicode code point preferable. </p><p>Where the character set is limited to <a href="/wiki/ASCII" title="ASCII">ASCII</a>, the <a href="/wiki/IEEE_Std_260.1-2004" title="IEEE Std 260.1-2004">IEEE 260.1</a> standard recommends using the unit name "ohm" as a symbol instead of Ω. </p><p>In the electronics industry it is common to use the character <i>R</i> instead of the Ω symbol, thus, a 10 Ω resistor may be represented as 10R. This is part of the <a href="/wiki/RKM_code" title="RKM code">RKM code</a>. It is used in many instances where the value has a decimal place. For example, 5.6 Ω is listed as 5R6, or 2200 Ω is listed as 2K2. This method avoids overlooking the decimal point, which may not be rendered reliably on components or when duplicating documents. </p><p><a href="/wiki/Unicode" title="Unicode">Unicode</a> encodes the symbol as <span class="nowrap"><style data-mw-deduplicate="TemplateStyles:r886049734">.mw-parser-output .monospaced{font-family:monospace,monospace}</style><span class="monospaced">U+2126</span> </span><span style="font-size:125%;line-height:1em">Ω</span> <span style="font-variant: small-caps; text-transform: lowercase; font-feature-settings: 'onum'">OHM SIGN</span>, distinct from Greek omega among <a href="/wiki/Letterlike_symbols" class="mw-redirect" title="Letterlike symbols">letterlike symbols</a>, but it is only included for backward compatibility and the Greek uppercase omega character <span class="nowrap"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734" /><span class="monospaced">U+03A9</span> </span><span style="font-size:125%;line-height:1em">Ω</span> <span style="font-variant: small-caps; text-transform: lowercase; font-feature-settings: 'onum'">GREEK CAPITAL LETTER OMEGA</span> (<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r886049734" /><span class="monospaced">&ohm;, &Omega;</span>) is preferred.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> In MS-DOS and Microsoft Windows, the <a href="/wiki/Alt_code" title="Alt code">alt code</a> ALT 234 may produce the Ω symbol. In Mac OS, <style data-mw-deduplicate="TemplateStyles:r1249182868">.mw-parser-output .keyboard-key{border:1px solid #aaa;border-radius:0.2em;box-shadow:0.1em 0.1em 0.2em rgba(0,0,0,0.1);background-color:var(--background-color-neutral-subtle,#f8f9fa);background-image:linear-gradient(to bottom,var(--background-color-neutral,#eaecf0),var(--background-color-neutral-subtle,#f8f9fa),var(--background-color-neutral,#eaecf0));color:var(--color-base,#202122);padding:0.1em 0.3em;font-family:inherit;font-size:0.85em}</style><kbd class="keyboard-key nowrap">⌥ Opt</kbd>+<kbd class="keyboard-key nowrap">Z</kbd> does the same. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=8" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Electronic_color_code" title="Electronic color code">Electronic color code</a>, used for indicating the value of resistors</li> <li><a href="/wiki/History_of_measurement" title="History of measurement">History of measurement</a></li> <li><a href="/wiki/International_Committee_for_Weights_and_Measures" class="mw-redirect" title="International Committee for Weights and Measures">International Committee for Weights and Measures</a></li> <li><a href="/wiki/Orders_of_magnitude_(resistance)" class="mw-redirect" title="Orders of magnitude (resistance)">Orders of magnitude (resistance)</a></li> <li><a href="/wiki/Resistivity" class="mw-redirect" title="Resistivity">Resistivity</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="Notes_and_references">Notes and references</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=9" title="Edit section: Notes and references"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-BIPM_SI9-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-BIPM_SI9_1-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf">BIPM SI Brochure: Appendix 1, p.46 (pdf)</a></span> </li> <li id="cite_note-SI10-2002-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-SI10-2002_2-0">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFSASB/SCC14_–_SCC14_–_Quantities,_Units,_and_Letter_Symbols2002" class="citation book cs1">SASB/SCC14 – SCC14 – Quantities, Units, and Letter Symbols (2002-12-30). <a rel="nofollow" class="external text" href="https://standards.ieee.org/ieee/SI_10/3286/"><i>IEEE/ASTM SI 10-2002: IEEE/ASTM Standard for Use of the International System of Units (SI): The Modern Metric System</i></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=IEEE%2FASTM+SI+10-2002%3A+IEEE%2FASTM+Standard+for+Use+of+the+International+System+of+Units+%28SI%29%3A+The+Modern+Metric+System.&rft.date=2002-12-30&rft.au=SASB%2FSCC14+%E2%80%93+SCC14+%E2%80%93+Quantities%2C+Units%2C+and+Letter+Symbols&rft_id=https%3A%2F%2Fstandards.ieee.org%2Fieee%2FSI_10%2F3286%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span><span class="cs1-maint citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_book" title="Template:Cite book">cite book</a>}}</code>: CS1 maint: multiple names: authors list (<a href="/wiki/Category:CS1_maint:_multiple_names:_authors_list" title="Category:CS1 maint: multiple names: authors list">link</a>) CS1 maint: numeric names: authors list (<a href="/wiki/Category:CS1_maint:_numeric_names:_authors_list" title="Category:CS1 maint: numeric names: authors list">link</a>)</span></span> </li> <li id="cite_note-Thompson-Taylor_2008-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-Thompson-Taylor_2008_3-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFThompsonTaylor2008" class="citation book cs1">Thompson, Ambler; Taylor, Barry N. (November 2008) [March 2008]. "Chapter 9.3 Spelling unit names with prefixes". <a rel="nofollow" class="external text" href="https://physics.nist.gov/cuu/pdf/sp811.pdf"><i>Guide for the Use of the International System of Units (SI)</i></a> <span class="cs1-format">(PDF)</span> (2nd corrected printing, 2008 ed.). Gaithersburg, Maryland, USA: <a href="/wiki/National_Institute_of_Standards_and_Technology" title="National Institute of Standards and Technology">National Institute of Standards and Technology</a>, U.S. Department of Commerce. <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><a href="/wiki/CODEN_(identifier)" class="mw-redirect" title="CODEN (identifier)">CODEN</a> <a rel="nofollow" class="external text" href="https://cassi.cas.org/searching.jsp?searchIn=codens&exactMatch=y&c=WIy460-R_DY&searchFor=NSPUE3">NSPUE3</a>. NIST Special Publication 811. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20210131024615/https://physics.nist.gov/cuu/pdf/sp811.pdf">Archived</a> <span class="cs1-format">(PDF)</span> from the original on 2021-01-31<span class="reference-accessdate">. Retrieved <span class="nowrap">2021-01-31</span></span>. p. 31: <q>Reference <a href="#SI10-2002">[6]</a> points out that there are three cases in which the final vowel of an SI prefix is commonly omitted: megohm (not megaohm), kilohm (not kiloohm), and hectare (not hectoare). In all other cases in which the unit name begins with a vowel, both the final vowel of the prefix and the vowel of the unit name are retained and both are pronounced.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Chapter+9.3+Spelling+unit+names+with+prefixes&rft.btitle=Guide+for+the+Use+of+the+International+System+of+Units+%28SI%29&rft.place=Gaithersburg%2C+Maryland%2C+USA&rft.pages=31&rft.edition=2nd+corrected+printing%2C+2008&rft.pub=National+Institute+of+Standards+and+Technology%2C+U.S.+Department+of+Commerce&rft.date=2008-11&rft.aulast=Thompson&rft.aufirst=Ambler&rft.au=Taylor%2C+Barry+N.&rft_id=https%3A%2F%2Fphysics.nist.gov%2Fcuu%2Fpdf%2Fsp811.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span> (85 pages)</span> </li> <li id="cite_note-NIST_2016-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-NIST_2016_4-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-9-rules-and-style-conventions-spelling-unit-names">"NIST Guide to the SI"</a>. Gaithersburg, Maryland, USA: <a href="/wiki/National_Institute_of_Standards_and_Technology" title="National Institute of Standards and Technology">National Institute of Standards and Technology</a> (NIST), Physical Measurement Laboratory. 2016-08-25 [2016-01-28]. Chapter 9: Rules and Style Conventions for Spelling Unit Names, 9.3: Spelling unit names with prefixes. Special Publication 811. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20210131024623/https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-9-rules-and-style-conventions-spelling-unit-names">Archived</a> from the original on 2021-01-31<span class="reference-accessdate">. Retrieved <span class="nowrap">2021-01-31</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=NIST+Guide+to+the+SI&rft.place=Gaithersburg%2C+Maryland%2C+USA&rft.pages=Chapter+9%3A+Rules+and+Style+Conventions+for+Spelling+Unit+Names%2C+9.3%3A+Spelling+unit+names+with+prefixes&rft.pub=National+Institute+of+Standards+and+Technology+%28NIST%29%2C+Physical+Measurement+Laboratory&rft.date=2016-08-25&rft_id=https%3A%2F%2Fwww.nist.gov%2Fpml%2Fspecial-publication-811%2Fnist-guide-si-chapter-9-rules-and-style-conventions-spelling-unit-names&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span> <a rel="nofollow" class="external autonumber" href="http://physics.nist.gov/Pubs/SP811/sec09.html">[1]</a></span> </li> <li id="cite_note-Aubrecht-French-Iona_2012-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-Aubrecht-French-Iona_2012_5-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFAubrecht_IIFrenchIona2012" class="citation journal cs1">Aubrecht II, Gordon J.; French, Anthony P.; Iona, Mario (2012-01-20). "About the International System of Units (SI) Part IV. Writing, Spelling, and Mathematics". <i><a href="/wiki/The_Physics_Teacher" title="The Physics Teacher">The Physics Teacher</a></i>. <b>50</b> (2): <span class="nowrap">77–</span>79. <a href="/wiki/Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2012PhTea..50...77A">2012PhTea..50...77A</a>. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1119%2F1.3677278">10.1119/1.3677278</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+Physics+Teacher&rft.atitle=About+the+International+System+of+Units+%28SI%29+Part+IV.+Writing%2C+Spelling%2C+and+Mathematics&rft.volume=50&rft.issue=2&rft.pages=%3Cspan+class%3D%22nowrap%22%3E77-%3C%2Fspan%3E79&rft.date=2012-01-20&rft_id=info%3Adoi%2F10.1119%2F1.3677278&rft_id=info%3Abibcode%2F2012PhTea..50...77A&rft.aulast=Aubrecht+II&rft.aufirst=Gordon+J.&rft.au=French%2C+Anthony+P.&rft.au=Iona%2C+Mario&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span></span> </li> <li id="cite_note-Hunt_1994-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-Hunt_1994_6-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFHunt1994" class="citation journal cs1">Hunt, Bruce J. (1994). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20140308030456/https://webspace.utexas.edu/huntbj/1994-Ohm-Osiris.pdf">"The Ohm Is Where the Art Is: British Telegraph Engineers and the Development of Electrical Standards"</a> <span class="cs1-format">(PDF)</span>. <i>Osiris</i>. 2. <b>9</b>: <span class="nowrap">48–</span>63. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F368729">10.1086/368729</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:145557228">145557228</a>. Archived from <a rel="nofollow" class="external text" href="https://liberalarts.utexas.edu/hps/publications/index.php">the original</a> on 2014-03-08<span class="reference-accessdate">. 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H.</a>; <a href="/wiki/Augustus_Matthiessen" title="Augustus Matthiessen">Matthiessen, A.</a>; <a href="/wiki/Fleeming_Jenkin" title="Fleeming Jenkin">Jenkin, Fleeming</a> (September 1862). <a rel="nofollow" class="external text" href="https://www.biodiversitylibrary.org/page/29361871#page/192/mode/2up"><i>Provisional Report of the Committee appointed by the British Association on Standards of Electrical Resistance</i></a>. Thirty-second Meeting of the British Association for the Advancement of Science. London: John Murray. pp. <span class="nowrap">125–</span>163<span class="reference-accessdate">. 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London: John Murray. p. Foldout facing page 349<span class="reference-accessdate">. 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C.; <a href="/wiki/Josiah_Latimer_Clark" title="Josiah Latimer Clark">Clark, Latimer</a>; Forbes, D.; Hockin, Charles; <a href="/wiki/James_Prescott_Joule" title="James Prescott Joule">Joule, James Prescott</a> (September 1867). <a rel="nofollow" class="external text" href="https://www.biodiversitylibrary.org/item/93115#page/578/mode/1up"><i>Report of the Committee on Standards of Electrical Resistance</i></a>. Thirty-seventh Meeting of the British Association for the Advancement of Science. London: John Murray. p. 488<span class="reference-accessdate">. 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Retrieved <span class="nowrap">2023-12-23</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Nature&rft.atitle=The+Electrical+Congress+Of+Paris%2C+1884&rft.volume=30&rft.issue=758&rft.pages=%3Cspan+class%3D%22nowrap%22%3E26-%3C%2Fspan%3E27&rft.date=1884-05&rft_id=info%3Adoi%2F10.1038%2F030026a0&rft_id=https%3A%2F%2Fwww.nature.com%2Farticles%2F030026a0&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span></span> </li> <li id="cite_note-eb11-p742-14"><span class="mw-cite-backlink">^ <a href="#cite_ref-eb11-p742_14-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-eb11-p742_14-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFFleming1911" class="citation encyclopaedia cs1"><a href="/wiki/John_Ambrose_Fleming" title="John Ambrose Fleming">Fleming, John Ambrose</a> (1911). <span class="cs1-ws-icon" title="s:1911 Encyclopædia Britannica/Units, Physical"><a class="external text" href="https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Units,_Physical">"Units, Physical" </a></span>. In <a href="/wiki/Hugh_Chisholm" title="Hugh Chisholm">Chisholm, Hugh</a> (ed.). <i><a href="/wiki/Encyclop%C3%A6dia_Britannica_Eleventh_Edition" title="Encyclopædia Britannica Eleventh Edition">Encyclopædia Britannica</a></i>. Vol. 27 (11th ed.). Cambridge University Press. pp. <span class="nowrap">738–</span>745, see page 742. <q>An Electrical Congress was held in Chicago, U.S.A. in August 1893, to consider......and at the last one held in London in October 1908 were finally adopted</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Units%2C+Physical&rft.btitle=Encyclop%C3%A6dia+Britannica&rft.pages=%3Cspan+class%3D%22nowrap%22%3E738-%3C%2Fspan%3E745%2C+see+page+742&rft.edition=11th&rft.pub=Cambridge+University+Press&rft.date=1911&rft.aulast=Fleming&rft.aufirst=John+Ambrose&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span></span> </li> <li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text">Gordon Wigan (trans. and ed.), <i>Electrician's Pocket Book</i>, Cassel and Company, London, 1884</span> </li> <li id="cite_note-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-16">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://books.google.com/books?id=OkxGT9mfNGkC&dq=%22Siemens+mercury+unit%22&pg=PA32">Historical Studies in International Corporate Business. Teich p34</a></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text">R. Dzuiba and others, <i>Stability of Double-Walled Maganin Resistors</i> in <i>NIST Special Publication Proceedings of SPIE</i>, The Institute, 1988 pp. 63–64</span> </li> <li id="cite_note-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-18">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFPreece1867" class="citation cs2">Preece, William Henry (1867), <a rel="nofollow" class="external text" href="https://books.google.com/books?id=6Yg7AQAAMAAJ&q=ohm+preece+symbol&pg=PA397">"The B.A. unit for electrical measurements"</a>, <i><a href="/wiki/Philosophical_Magazine" title="Philosophical Magazine">Philosophical Magazine</a></i>, vol. 33, p. 397<span class="reference-accessdate">, retrieved <span class="nowrap">2017-02-26</span></span></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Philosophical+Magazine&rft.atitle=The+B.A.+unit+for+electrical+measurements&rft.volume=33&rft.pages=397&rft.date=1867&rft.aulast=Preece&rft.aufirst=William+Henry&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D6Yg7AQAAMAAJ%26q%3Dohm%2Bpreece%2Bsymbol%26pg%3DPA397&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span></span> </li> <li id="cite_note-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-19">^</a></b></span> <span class="reference-text">E.g. recommended in HTML 4.01: <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.w3.org/TR/html401/sgml/entities.html#h-24.1">"HTML 4.01 Specification"</a>. <i>W3C</i>. 1998. 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Retrieved <span class="nowrap">2018-11-22</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=W3C&rft.atitle=HTML+4.01+Specification&rft.pages=Section+24.1+%22Introduction+to+character+entity+references%22&rft.date=1998&rft_id=http%3A%2F%2Fwww.w3.org%2FTR%2Fhtml401%2Fsgml%2Fentities.html%23h-24.1&rfr_id=info%3Asid%2Fen.wikipedia.org%3AOhm" class="Z3988"></span></span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text">Excerpts from <i><a rel="nofollow" class="external text" href="https://www.unicode.org/versions/Unicode4.0.0/ch07.pdf#search=%22character%20U%2B2126%20maps%20OR%20map%20OR%20mapping%22">The Unicode Standard, Version 4.0</a></i>, accessed 11 October 2006</span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Ohm&action=edit&section=10" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="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</a></li> <li><a rel="nofollow" class="external text" href="http://www.bipm.fr/en/si/si_brochure/">Official SI brochure</a></li> <li><a rel="nofollow" class="external text" href="http://physics.nist.gov/Pubs/SP811/contents.html">NIST Special Publication 811</a></li> <li><a rel="nofollow" class="external text" href="http://www.sizes.com/units/ohm.htm">History of the ohm at sizes.com</a></li> <li><a rel="nofollow" class="external text" href="http://seaus.free.fr/spip.php?article964">History of 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href="/wiki/SI_base_unit" title="SI base unit">Base units</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ampere" title="Ampere">ampere</a></li> <li><a href="/wiki/Candela" title="Candela">candela</a></li> <li><a href="/wiki/Kelvin" title="Kelvin">kelvin</a></li> <li><a href="/wiki/Kilogram" title="Kilogram">kilogram</a></li> <li><a href="/wiki/Metre" title="Metre">metre</a></li> <li><a href="/wiki/Mole_(unit)" title="Mole (unit)">mole</a></li> <li><a href="/wiki/Second" title="Second">second</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/SI_derived_unit" title="SI derived unit">Derived units <br />with special names</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Becquerel" title="Becquerel">becquerel</a></li> <li><a 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definitions of the SI base units">Historical definitions of the SI base units</a></li> <li><a href="/wiki/2019_revision_of_the_SI" title="2019 revision of the SI">2019 revision of the SI</a></li> <li><a href="/wiki/System_of_units_of_measurement" title="System of units of measurement">System of units of measurement</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/wiki/Category:SI_units" 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