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In direct current (DC) circuits, this product is equal to the real power, measured in watts. [3] The volt-ampere is dimensionally equivalent to the watt: in SI units, 1 V⋅A = 1 W. VA rating is most used for generators and transformers, and other power handling equipment, where loads may be reactive (inductive or capacitive).
In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit).
An ampere-hour or amp-hour (symbol: A⋅h or A h; often simplified as Ah) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3,600 coulombs. [1] [2]
The power gain can be calculated using voltage instead of power using Joule's first law = /; the formula is: = . In many cases, the input impedance and output impedance are equal, so the above equation can be simplified to:
Electricity usage is often given in units of kilowatt-hours per year or other periods. [4] This is a measurement of average power consumption, meaning the average rate at which energy is transferred. One kilowatt-hour per year is around 0.11 watts.
For most audio applications more power is needed at low frequencies. This requires a high-power amplifier for low frequencies (e.g., 200 watts for 20–200 Hz band), lower power amplifier for the midrange (e.g., 50 watts for 200 to 1000 Hz), and even less the high end (e.g. 5 watts for 1000–20000 Hz).
An important property of three-phase power is that the instantaneous power available to a resistive load, = =, is constant at all times.Indeed, let = = To simplify the mathematics, we define a nondimensionalized power for intermediate calculations, =
Electric power is the rate of transfer of electrical energy within a circuit.Its SI unit is the watt, the general unit of power, defined as one joule per second.Standard prefixes apply to watts as with other SI units: thousands, millions and billions of watts are called kilowatts, megawatts and gigawatts respectively.