ohm

1 a unit of electrical resistance equal to the resistance between two points on a conductor when a potential difference of one volt between them produces a current of one ampere

2 German physicist who formulated Ohm's Law (1787-1854) [syn: Georg Simon Ohm]

English

Etymology

Named after the German physicist Georg Ohm.

Pronunciation

• Rhymes: -əʊm

Noun

1. In the International System of Units, the derived unit of electrical resistance; the electrical resistance of a device across which a potential difference of one volt causes a current of one ampere. Symbol: Ω

Translations

Dutch

Noun

ohm , (plural: ohms, diminutive: ohmpje, plural diminutive: ohmpjes)

1. ohm

Usage notes

The plural is not actually used. A resistance is actually expressed as De weerstand bedraagt 56 ohm.

French

Pronunciation

Noun

ohm

1. ohm

The ohm (symbol: Ω) is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg Ohm.

Definition

The ohm is the electric resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere, the conductor not being the seat of any electromotive force.

\Omega = \dfrac = \dfrac

Conversions

• A measurement in ohms is the reciprocal of a measurement in siemens, the SI unit of electrical conductance. Note that 'siemens' is both singular and plural. The non-SI unit, the mho (ohm written backwards), is equivalent to siemens but is mostly obsolete and rarely used.
• Ohms to watts: The power dissipated by a resistor may be calculated using resistance and voltage. The formula is a combination of Ohm's law and Joule's law:

P=

where P is the power in watts, R is the resistance in ohms and V is the voltage across the resistor.

This method is not reliable for determining the power of an incandescent light bulb, resistance heater or electric short since all these devices operate at high temperatures and the resistance measured using a meter will not represent the operating resistance. For these conditions instead multiply V by current in amperes to get power in watts.

References and notes

See also

• Ohm's law
• Resistor
• abohm

External links

• Scanned books of Georg Simon Ohm at the library of the University of Applied Sciences Nuernberg
• Official SI brochure
• NIST Special Publication 811
• History of the ohm at sizes.com