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Ohm | Electricity, Resistance & Voltage | Britannica Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos ohm Introduction References & Edit History Quick Facts & Related Topics Videos Quizzes Fun Facts of Measurement & Math Contents CITE verified Cite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/science/ohm Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback Our editors will review what you’ve submitted and determine whether to revise the article. External Websites NIST - Metrology of the Ohm All About circuits - Ohm�s Law - How Voltage, Current, and Resistance Relate IEEE Xplore - Standardization of the Ohm as a Unit of Electrical Resistance, 1861�1867 ohm unit of energy measurement Ask Anything Homework Help Also known as: Ω Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything ohm , abbreviation Ω, unit of electrical resistance in the metre-kilogram-second system, named in honour of the 19th-century German physicist Georg Simon Ohm . It is equal to the resistance of a circuit in which a potential difference of one volt produces a current of one ampere (1Ω = 1 V / A ); or, the resistance in which one watt of power is dissipated when one ampere flows through it. Ohm’s law ( q.v. ) states that resistance equals the ratio of the potential difference to current, and the ohm, volt, and ampere are the respective fundamental units used universally for expressing quantities. Key People: Fleeming Jenkin Henry Augustus Rowland (Show more) Related Topics: International System of Units resistance electrical impedance megohm unit (Show more) See all related content Impedance , the apparent resistance to an alternating current , and reactance , the part of impedance resulting from capacitance or inductance , are circuit characteristics that are measured in ohms. The acoustic ohm and the mechanical ohm are analogous units sometimes used in the study of acoustic and mechanical systems, respectively.