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The volt-ampere (SI symbol: VA, [1] sometimes V⋅A or V A) is the unit of measurement for apparent power in an electrical circuit. It is the product of the root mean square voltage (in volts) and the root mean square current (in amperes). [2] Volt-amperes are usually used for analyzing alternating current (AC) circuits.
The ampere is named for French physicist and mathematician André-Marie Ampère (1775–1836), who studied electromagnetism and laid the foundation of electrodynamics.In recognition of Ampère's contributions to the creation of modern electrical science, an international convention, signed at the 1881 International Exposition of Electricity, established the ampere as a standard unit of ...
Ohm's law states that the electric current through a conductor is proportional to the voltage across it, with a constant of proportionality called resistance. The law was named after Georg Ohm, who published his experimental results in 1827 and explained them with a model of internal resistance.
A watt is the SI unit of power or radiant flux, equal to 1 joule per second or 1 kg⋅m 2 ⋅s −3. It is named after James Watt, an 18th-century inventor who improved the steam engine. Learn how to calculate watt, see examples, and explore its multiples and submultiples.
A coulomb (C) is the amount of electric charge delivered by a 1 ampere current in 1 second. It is defined in terms of the elementary charge e, which is about 6.241 509 × 1018 e.
Standard prefixes apply to watts as with other SI units: thousands, millions and billions of watts are called kilowatts, megawatts and gigawatts respectively. In common parlance, electric power is the production and delivery of electrical energy, an essential public utility in much of the world.
They made the volt equal to 10 8 cgs units of voltage, the cgs system at the time being the customary system of units in science. They chose such a ratio because the cgs unit of voltage is inconveniently small and one volt in this definition is approximately the emf of a Daniell cell , the standard source of voltage in the telegraph systems of ...
where X denotes reactance (units in ohms, Ω) of the load. Combining, the complex power (units in volt-amps, VA) is back-derived as = +, and the apparent power (units in volt-amps, VA) as | | = +. These are simplified diagrammatically by the power triangle.