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Encyclopedia > Electric power

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt. Transmission lines in Lund, Sweden Electric company redirects here. ... In physics, power (symbol: P) is the rate at which work is performed or energy is transferred. ... Electrical energy can refer to several closely related things. ... An electrical network or electrical circuit is an interconnection of analog electrical elements such as resistors, inductors, capacitors, diodes, switches and transistors. ... Look up si, Si, SI in Wiktionary, the free dictionary. ... The watt (symbol: W) is the SI derived unit for power. ...

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.

When electric current flows in a circuit with resistance, it does work. Devices convert this work into many useful forms, such as heat (electric heaters), light (light bulbs), motion (electric motors) and sound (loudspeaker). Electricity can be produced by generation or from storage such as batteries. Download high resolution version (582x800, 73 KB)Electrical Grid tower and cables PD File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (582x800, 73 KB)Electrical Grid tower and cables PD File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... “Pylon” redirects here. ... For other uses, see Brisbane (disambiguation). ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... For other uses, see Heat (disambiguation) In physics, heat, symbolized by Q, is energy transferred from one body or system to another due to a difference in temperature. ... A furnace is a device for heating air or any other fluid. ... This article does not cite any references or sources. ... The light bulb is one of the most significant inventions in the history of the human race, illuminating the darkness of the evening and bringing light indoors at all times in order focus on the task at hand. ... The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ... For other kinds of motors, see motor. ... Sound is a disturbance of mechanical energy that propagates through matter as a wave. ... For the Marty Friedman album, see Loudspeaker (album) An inexpensive low fidelity 3. ... World-wide electricity production for 1980 to 2005. ... Ffestiniog pumped storage power station upper reservoir Grid energy storage lets energy producers send excess electricity over the electricity transmission grid to temporary electricity storage sites that become energy producers when electricity demand is greater. ... Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams. ...

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 electrical and mechanical energy were interchangeable. Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... Joules law (also known as Joule effect) is a physical law expressing the relationship between the heat generated by the current flowing through a conductor. ... James Prescott Joule (December 24, 1818–October 11, 1889) was an English physicist, born in Salford, near Manchester. ...

. P = I V ,

where

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

For example: For other uses, see Watt (disambiguation). ... For other uses, see Ampere (disambiguation). ... Josephson junction array chip developed by NIST as a standard volt. ...

 2,mbox{A} cdot 12,mbox{V} = 24,mbox{W} , .

Joule's law can be combined with Ohm's law to produce two more equations: A voltage source, V, drives an electric current, I , through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference (i. ...

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

where

R is the resistance (Ohm or Ω).

For example: Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ... A multimeter can be used to measure resistance in ohms. ...

 (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. 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). That portion of power flow due to stored energy, that returns to the source in each cycle, is known as reactive power. Usually hidden to the unaided eye, the blinking of (non-incandescent) lighting powered by AC mains is revealed in this motion-blurred long exposure of city lights. ... An electric current i flowing around a circuit produces a magnetic field and hence a magnetic flux Φ through the circuit. ... Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. ... Real Power is often described as true power (or effective power) and is used by engineers to describe the actual amount of power present in a system, it is expressed in watts (W). ... Reactive power is an abstract quantity, typically used by power engineers to describe a certain type of energy flow in an electric distribution system. ...

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. 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: Image File history File links Power_Triangle_01. ... Usually hidden to the unaided eye, the blinking of (non-incandescent) lighting powered by AC mains is revealed in this motion-blurred long exposure of city lights. ... In mathematics, the Pythagorean theorem (AmE) or Pythagoras theorem (BrE) is a relation in Euclidean geometry among the three sides of a right triangle. ...

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

The ratio of real power to apparent power is called power factor and is a number always between 0 and 1.


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: This article is about the concept of integrals in calculus. ... This article is about vectors that have a particular relation to the spatial coordinates. ... For the cross product in algebraic topology, see Künneth theorem. ...

 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. In mathematics, a surface integral is a definite integral taken over some surface that may be a curved set in space; it can be thought of as the double integral analog of the path integral. ... The Poynting vector describes the energy flux (J·m−2·s−1) of an electromagnetic field. ...


See also

Energy Portal

Usually hidden to the unaided eye, the blinking of (non-incandescent) lighting powered by AC mains is revealed in this motion-blurred long exposure of city lights. ... Image File history File links Portal. ... World power usage in terawatts (TW), 1965-2005. ...

Power generation

World-wide electricity production for 1980 to 2005. ... Higher electricity use per capita correlates with a higher score on the Human Development Index(1997). ... This article is about applications of nuclear fission reactors as power sources. ... Mohave Generating Station, a 1,580 MW coal power plant near Laughlin, Nevada A fossil fuel power plant is an energy conversion center that burns fossil fuels to produce electricity, designed on a large scale for continuous operation. ...

References

  • Key Facts About the Electric Power Industry, Edison Electric Institute website
  • Reports on August 2003 Blackout, North American Electric Reliability Council website
  • Croft, Terrell; Summers, Wilford I. (1987). American Electricans' Handbook, Eleventh Edition, New York: McGraw Hill. ISBN 0-070-13932-6. 
  • Fink, Donald G.; Beaty, H. Wayne (1978). Standard Handbook for Electrical Engineers, Eleventh Edition, New York: McGraw Hill. ISBN 0-070-20974-X. 

External links

  • Electric power calculations

  Results from FactBites:
 
Electric power transmission - Wikipedia, the free encyclopedia (2466 words)
Typically power transmission is between the power plant and a substation in the vicinity of a populated area.
Power is transmitted underground in densly populated areas (such as large cities) but is typically avoided due to the high capacitive and resistive losses incurred.
AC power transmission is the transmission of electric power by alternating current.
  More results at FactBites »

 
 

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