Volt-ampere

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Volt-ampere

A volt-ampere in electrical terms, is the amount of power in an alternating current

Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
(AC) circuit equal to a current flow of one ampere

Ampere

The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....
at an electromotive force

Electromotive force

Electromotive force is a term used to characterize electrical devices, such as voltaic cells, Thermoelectric effects, electrical generators and transformers, and even resistors....
of one volt

Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
. It is equivalent to watt

WATT

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A volt-ampere in electrical terms, is the amount of power in an alternating current

Alternating current

Ampere

Electromotive force

Electromotive force is a term used to characterize electrical devices, such as voltaic cells, Thermoelectric effects, electrical generators and transformers, and even resistors....
of one volt

Volt

WATT

WATT is a radio station broadcasting a News radio-Talk radio-Sports radio format. Licensed to Cadillac, Michigan, it first began broadcasting in 1945....
s for non-reactive circuits and in the strictest sense is identical, but by convention the two are used as units for subtly different physical quantities.

The instantaneous real power delivered to any load is the voltage across the load at a given instant times the current through the load at that same instant. Making such a measurement requires an instrument that can make simultaneous instantaneous measurements of current and voltage. If separate current and voltage instruments that are incapable of coordinating their measurements are used, and which give root mean square

Root mean square

In mathematics, the root mean square , also known as the quadratic mean, is a statistics measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids....
measurements, and the two measurements are multiplied, the result will be apparent power; for reactive loads (loads containing capacitance

Capacitance

In electromagnetism and electronics, capacitance is the ability of a body to hold an electrical charge.Capacitance is also a measure of the amount of electric charge stored for a given electric potential....
or inductance

Inductance

Inductance is the property in an electrical circuit where a change in the current flowing through that circuit induces an Electromotive force that opposes the change in current ....
), apparent power is greater than real power. By convention, the unit of measure for apparent power is the volt-ampere. For resistive loads

Electrical resistance

The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material....
, real power equals apparent power; incandescent lights, electric heating elements, and toaster

Toaster

A toaster is a small electric kitchen appliance designed to toast multiple types of bread products. A typical modern two-slice toaster draws anywhere between 600 and 1200 Watt and makes toast in 1 to 3 minutes....
s are examples of nearly resistive loads. (Ciletti et al. 1993, 82, for incandescent lights)

While the volt-ampere (abbreviated VA) and the watt are dimensionally equivalent one may find products rated in both VAs and watts with different numbers. This is common practice on UPSs (Uninterruptible Power Supplies).

Uninterruptible power supply

An uninterruptible power supply , also known as a battery back-up, provides emergency power and, depending on the topology, line regulation as well to connected equipment by supplying power from a separate source when utility power is not available....
The VA rating is the apparent power that a UPS is capable of producing, while the watt rating is the real power (or true power)

AC power

This article deals with power in AC systems. See Mains electricity for information on utility-supplied AC power.Power is defined as the rate of flow of energy past a given point....
it is capable of producing, as opposed to reactive power. In the type of loads often used with UPSs, such as computers, the apparent power used (volt-amperes) will be larger than the true power used (watts). The ratio of these two quantities is called the power factor

Power factor

The power factor of an alternating current electric power system is defined as the ratio of the AC power flowing to the load to the AC power , and is a number between 0 and 1 ....
.

Volt-ampere

See also