The ohm is the SI derived unit of electrical resistance (derived from the ampere and the watt). Its symbol is the Greek capital letter omega (Ω). The ohm is named for Georg Ohm, a German physicist who discovered the relation between voltage and current, expressed in Ohm's Law.By definition from Ohm's Law, a device has a resistance of one ohm if a voltage of one volt will cause a current of one ampere to flow (R = V/I). Alternatively and equivalently, a device that dissipates one watt of power with one ampere of current flowing through it has a resistance of one ohm (R = P/I2).
One thousand ohms is called a kilohm (not kilo-ohm), and abbreviated kΩ. One million ohms is called a megohm (not mega-ohm), and abbreviated MΩ. Other orders of magnitude follow standard SI conventions.
A measurement in ohms is the reciprocal of a measurement in siemens, the SI unit of electrical conductanceElectrical conductance is the reciprocal of electrical resistance. The SI derived unit of conductance is the siemens (symbol S, equal to 1/Ω). Electrical conductance should not be confused with electrical conductivity, which is material specific fea. Note that 'siemens' is both singularWhen used as a simple adjective in English, singular usually means unique. The singular is one of two grammatical numbers in English; the other is the plural . In mathematics singular has a number of meanings A square matrix is called singular if it is no and pluralPlural is a grammatical number, typically referring to more than one of the referent in the real world. In the English language, singular and plural are the only grammatical numbers. In English, nouns, pronouns, and demonstratives inflect for plurality.. The reciprocal of the ohm is also called the mho, from ohm written backwards.
The complexThe complex numbers are an extension of the real numbers, in which all non-constant polynomials have roots. The complex numbers contain a number , the imaginary unit with , i. is a square root of. Every complex number can be represented in the form , wher quantity impedanceIn electrical engineering, impedance is a measure for the manner and degree a component resists the flow of electrical current if a given voltage is applied. It is denoted by the symbol Z and is measured in ohms. Impedance differs from simple resistance i is a generalisation of resistance. Its real part is resistance and its imaginary part is reactanceIn the analysis of an alternating-current electrical circuit (for example a RLC series circuit), reactance is the imaginary part of impedance, and is caused by the presence of inductors or capacitors in the circuit. Reactance is denoted by the symbol X an. For consistency, impedance, resistance and reactance all have units of ohms.
The ohm is since 1990 maintained internationally using the quantum Hall effectThe quantum Hall effect is a quantum mechanical version of the Hall effect, observed in two-dimensional systems of electrons subjected to low temperatures and strong magnetic fields, in which the Hall conductance sigma takes on the quantized values : wher, where a conventional value is used for the ' von-Klitzing constant', fixed by the 18th CGPM as
R{K-90} = 25812.807 Ω.
1 SI electricity units
