Ohm: Difference between revisions
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The '''ohm''', abbreviated '''Ω''', is the [[SI]] unit of [[electrical resistance]]. It is the resistance which will allow a current of one [[ampere]] across a potential drop of one [[volt]]. | {{subpages}} | ||
The '''ohm''', abbreviated '''Ω'''([[Omega]]), is the [[SI]] unit of [[electrical resistance]]. It is the resistance which will allow a current of one [[ampere]] across a potential drop of one [[volt]]. | |||
The ohm is named for [[Georg Ohm]] (1789 - 1854), an early investigator of electricity, who determined the relation between current, potential, and resistance, now called [[Ohm's Law]]. | The ohm is named for [[Georg Ohm]] (1789 - 1854), an early investigator of electricity, who determined the relation between current, potential, and resistance, now called [[Ohm's Law]]. | ||
The ohm is a derived unit in the SI, equal to 1 [[volt|V]]/[[ampere|A]]; or in terms of SI basic units: | The ohm is a derived unit in the SI, equal to 1 [[volt|V]]/[[ampere|A]]; or in terms of SI basic units: | ||
<math>\Omega = m^2 \cdot kg \cdot s^{-3} \cdot A^{-2} = \frac{m^2 \cdot kg}{s^{3} \cdot A^{2}} </math>. | |||
==Other definitions== | ==Other definitions== | ||
The "international ohm" was defined in 1893 (at the International Electrical Conference) as the resistance of a column of mercury of constant cross section at the temperature of melting ice, 106.3 centimeters long and with a mass of 14.4521 grams (which gave a cross-section of 1 square millimeter). | The "international ohm" was defined in 1893 (at the International Electrical Conference) as the resistance of a column of mercury of constant cross section at the temperature of melting ice, 106.3 centimeters long and with a mass of 14.4521 grams (which gave a cross-section of 1 square millimeter). | ||
In 1990, the [[CIPM]] recommended that a conventional value of 25812.807 Ω be used for the [[von Klitzing constant]] <math>\scriptstyle | In 1990, the [[CIPM]] recommended that a conventional value of 25812.807 Ω be used for the [[von Klitzing constant]] <math>\scriptstyle h/e^2</math> (where ''h'' is [[Planck's constant]] and ''e'' is the elementary charge), which makes calibration easy using the [[quantum Hall effect]]. This is technically not a redefinition, but allows for increased precision in measurement. | ||
==Sources== | ==Sources== | ||
*{{cite web|url=http://www.sizes.com/units/ohm.htm|title=Ohm|publisher=Sizes.com|date=2005-02-14|accessdate=2007-06-23}} | *{{cite web|url=http://www.sizes.com/units/ohm.htm|title=Ohm|publisher=Sizes.com|date=2005-02-14|accessdate=2007-06-23}} | ||
*{{cite web|url=http://www.sizes.com/units/ohm_international.htm|title=International ohm|publisher=Sizes.com|date=2007-06-03|accessdate=2007-06-23}} | *{{cite web|url=http://www.sizes.com/units/ohm_international.htm|title=International ohm|publisher=Sizes.com|date=2007-06-03|accessdate=2007-06-23}} | ||
Latest revision as of 19:18, 3 March 2008
The ohm, abbreviated Ω(Omega), is the SI unit of electrical resistance. It is the resistance which will allow a current of one ampere across a potential drop of one volt.
The ohm is named for Georg Ohm (1789 - 1854), an early investigator of electricity, who determined the relation between current, potential, and resistance, now called Ohm's Law.
The ohm is a derived unit in the SI, equal to 1 V/A; or in terms of SI basic units:
.
Other definitions
The "international ohm" was defined in 1893 (at the International Electrical Conference) as the resistance of a column of mercury of constant cross section at the temperature of melting ice, 106.3 centimeters long and with a mass of 14.4521 grams (which gave a cross-section of 1 square millimeter).
In 1990, the CIPM recommended that a conventional value of 25812.807 Ω be used for the von Klitzing constant (where h is Planck's constant and e is the elementary charge), which makes calibration easy using the quantum Hall effect. This is technically not a redefinition, but allows for increased precision in measurement.
Sources
- Ohm. Sizes.com (2005-02-14). Retrieved on 2007-06-23.
- International ohm. Sizes.com (2007-06-03). Retrieved on 2007-06-23.