We are creating the world's most trusted encyclopedia and knowledge base.
Once you join us and log in, you'll be able to edit this page instantly!

Ohm

From Citizendium, the Citizens' Compendium

Jump to: navigation, search

Main Article

Talk

Definition ^[?]

Related Articles ^[?]

Bibliography ^[?]

External Links ^[?]

This is a draft article, under development. These unapproved articles are subject to a disclaimer.

[edit intro]

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:

$\Omega = m^2 \cdot kg \cdot s^{-3} \cdot A^{-2} = \frac{m^2 \cdot kg}{s^{3} \cdot A^{2}}$ .

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 $\scriptstyle h/e^2$ (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.