Ohm: Difference between revisions
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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== | ||
Revision as of 19:20, 3 August 2007
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.
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: Ω = m2·kg·s−3·A−2.
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.