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For delivered electrical power, see Electrical power industry.
For physics concept of expenditure of energy, see Power (physics). In Physics, power (symbol P) is the rate at which work is performed or energy is transmitted or the amount of energy required or expended for

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. Electric energy is the potential energy associated with the conservative Coulomb forces between Charged particles contained within a system, where An electrical network is an interconnection of Electrical elements such as Resistors Inductors Capacitors Transmission lines Voltage The SI unit of power is the watt. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.

Electrical power is distributed via cables and electricity pylons like these in Brisbane, Australia.
Electrical power is distributed via cables and electricity pylons like these in Brisbane, Australia. Brisbane ( is the state capital of Queensland. Brisbane is the third most populous city in Australia and the most populous city of Queensland For a topic outline on this subject see List of basic Australia topics.

When electric current flows in a circuit with resistance, it does work. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is Devices convert this work into many useful forms, such as heat (electric heaters), light (light bulbs), motion (electric motors) and sound (loudspeaker). In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Electric heating is any process in which electrical energy is converted to heat Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general The kinetic energy of an object is the extra Energy which it possesses due to its motion An electric motor uses Electrical energy to produce Mechanical energy. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies For the Marty Friedman album see Loudspeaker (album A loudspeaker, speaker, or speaker system is an electroacoustical Electricity can be produced by generation or from storage such as batteries. Electricity generation is the process of converting non-electrical Energy to Electricity. Grid energy storage is used to manage the flow of electrical energy In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy

Contents

Mathematics of electric power

In circuits

Electric power, like mechanical power, is represented by the letter P in electrical equations. The term wattage is used colloquially to mean "electric power in watts. "

In direct current resistive circuits, instantaneous electrical power is calculated using Joule's Law, which is named after the British physicist James Joule, who first showed that heat and mechanical energy were interchangeable. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is Joule's laws are a pair of laws concerning the heat produced by a current and the energy dependence of an Ideal gas to that of pressure volume and temperature respectively A physicist is a Scientist who studies or practices Physics. Physicists study a wide range of physical phenomena in many branches of physics spanning James Prescott Joule FRS (ˈdʒuːl December 24, 1818 &ndash October 11, 1889) was an English Physicist

P = V I \,

where

P is the power (watt or W)
V is the potential difference (volt or V)
I is the current (ampere or A)

For example:

2\,\mbox{A} \cdot 12\,\mbox{V} = 24\,\mbox{W} \, . The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second

Joule's law can be combined with Ohm's law to produce two more equations:

P = I^2 R\, = \frac{V^2}{R} \,

where

R is the resistance (Ohm or Ω). Ohm's law applies to Electrical circuits it states that the current through a conductor between two points is directly proportional to the Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance,

For example:

(2\,\mbox{A})^2 \cdot 6\,\Omega = 24\,\mbox{W} \,

and

\frac{(12\,\mbox{V)}^2}{6\,\Omega} = 24\,\mbox{W} \,

In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. This article deals with power in AC systems See Mains electricity for information on utility supplied AC power In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting Capacitance is a measure of the amount of Electric charge stored (or separated for a given Electric potential. The portion of power flow that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power (also referred to as active power). This article deals with power in AC systems See Mains electricity for information on utility supplied AC power That portion of power flow due to stored energy, that returns to the source in each cycle, is known as reactive power. This article deals with power in AC systems See Mains electricity for information on utility supplied AC power

Power triangle The components of AC power
Power triangle The components of AC power

The relationship between real power, reactive power and apparent power can be expressed by representing the quantities as vectors. This article deals with power in AC systems See Mains electricity for information on utility supplied AC power Real power is represented as a horizontal vector and reactive power is represented as a vertical vector. The apparent power vector is the hypotenuse of a right triangle formed by connecting the real and reactive power vectors. This representation is often called the power triangle. Using the Pythagorean Theorem, the relationship among real, reactive and apparent power is:

(apparent power)2 = (real power)2 + (reactive power)2

Real and reactive powers can also be calculated directly from the apparent power, when the current and voltage are both sinusoids with a known phase angle between them:

(real power) = (apparent power) * cos(theta)
(reactive power) = (apparent power) * sin(theta)

The ratio of real power to apparent power is called power factor and is a number always between 0 and 1. In Mathematics, the Pythagorean theorem ( American English) or Pythagoras' theorem ( British English) is a relation in Euclidean geometry The power factor of an AC electric power system is defined as the Ratio of the real power to the apparent power, and is a number between 0 and

In space

Electrical power flows wherever electric and magnetic fields exist in the same place. The simplest example of this is in electrical circuits, as the preceding section showed. In the general case, however, the simple equation P = IV must be replaced by a more complex calculation, the integral of the vector cross-product of the electrical and magnetic fields over a specified area, thus:

\mathbf{P} = \int_S \mathbf{E} \times \mathbf{H} \cdot \mathbf{dA}. \,

The result is a scalar since it is the surface integral of the Poynting vector. The European Space Agency 's INTErnational Gamma-Ray Astrophysics Laboratory ( INTEGRAL) is detecting some of the most energetic radiation that comes from space In Mathematics, the cross product is a Binary operation on two vectors in a three-dimensional Euclidean space that results in another vector which In Mathematics, a surface integral is a Definite integral taken over a Surface (which may be a curved set in Space) it can be thought In Physics, the Poynting vector can be thought of as representing the Energy Flux (in W/m2 of an Electromagnetic field.

See also

Power generation

References

External links

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