Difference between revisions of "Electricity" - New World Encyclopedia

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:''Separate-but related articles are [[Electrical energy]], and [[Electric power]]''
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{{electromagnetism}}
  
''''Electricity'''' is the term the early scientists used when they were actually referring to 'charge'. Present usage of the term 'electricity' has become confused. In addition to the [[electric charge]] definition, the word electricity has several popular definitions which are contradictory.  Many sources say that "electricity" is the quantity of electrical energy measured in joules or kilowatt-hours. Other sources call it the motion of charges within a conductor, and they measure the quantity of electricity in terms of [[amperes]]. Still others call a wide variety of electrical phenomena by this name, e.g., bioelectricity, piezoelectricity, triboelectricity, etc. It is advisable to be cautious when interpreting the term "electricity" in place of the more precise terms electric charge, electric current, electrical energy, etc.
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'''Electricity''' (from [[Greek language|Greek]] ήλεκτρον (electron) ''"amber"'') is a general term for the variety of phenomena resulting from the presence and flow of [[electric charge]]. Together with [[magnetism]], it constitutes the [[fundamental interaction]] known as [[electromagnetism]]. It includes several well-known [[physics|physical]] phenomena, such as [[lightning]], [[electric field]]s, and [[electric current]]s. Electricity requires setting up a [[electrical circuit|circuit]] between positively charged and negatively charged poles. As such, it is a prime example of a general principle that energy of any kind is predicated upon the relationship between subject and object entities.  
[[image:Lightning.jpg|250px|thumb|right|[[Lightning]] strikes during a night-time thunderstorm.]]
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{{toc}}
== Electric charge ==
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Human ability to harness electricity is one of the keys for the establishment of modern technological society. Thus, electricity is used for lighting, communications, transportation, industrial machinery, power tools, appliances, elevators, computers, and an expanding variety of electronic goods.
[[Electric charge]] is a property of certain [[subatomic particle]]s (e.g., [[electron]]s and [[proton]]s) which interacts with [[electromagnetic fields]] and causes attractive and repulsive [[force]]s between them.
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[[Image:Lightning_NOAA.jpg|300px|thumb|right|[[Lightning]] strikes during a night-time [[thunderstorm]]. As powerful electric currents flow through the [[Earth's atmosphere]], energy is radiated as light.]]
Electric charge gives rise to one of the four [[fundamental force]]s of nature, and is a conserved property of [[matter]] that can be quantified.  In this sense, the phrase "[[quantity of electricity]]" is used interchangeably with the phrases "[[electric charge|charge of electricity]]" and "quantity of charge." There are two types  or charge: we call one kind of charge positive and the other negative. Through experimentation, we find that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by [[Coulomb's law]]. Some electrical effects are discussed under [[electrical phenomenon]] and [[electromagnetism]].
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== History of electricity ==
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The ancient [[Ancient Greece|Greeks]] and [[Parthia]]ns knew of static electricity from rubbing objects against fur. The ancient [[Babylonian Empire|Babylonia]]ns may have had some knowledge of [[electroplating]], based on the discovery of the Baghdad Battery,<ref>BBC News, [http://news.bbc.co.uk/1/hi/sci/tech/2804257.stm Riddle of 'Baghdad's batteries.’] Retrieved June 27, 2007.</ref> which resembles a [[Galvanic cell]].
  
The [[SI]] unit of charge is the [[coulomb]], which has the abbreviation "C".  The symbol ''Q'' is used in equations to represent the [[quantity of electricity]] or charge.  For example, "''Q'' = 0.5 C" means "the quantity of electric charge is 0.5 coulomb."
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[[Image:Saint Stephen's church plaque.png|thumb|left|[[Banjamin Franklin|Franklin]] kite plaque at Saint Stephen's Church, Philadelphia]]
  
== History ==
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It was Italian physician [[Girolamo Cardano]] in ''De Subtilitate'' (1550) who is credited with distinguishing, perhaps for the first time, between electrical and magnetic forces. In 1600, the English scientist [[William Gilbert]], in ''De Magnete,'' expanded on Cardano's work and coined the New Latin word ''electricus'' from ''{{polytonic|ἤλεκτρον}}'' ''(elektron)'', the Greek word for "amber." The first usage of the word ''electricity'' is ascribed to [[Sir Thomas Browne]] in his 1646 work, ''Pseudodoxia Epidemica''.  
===Ancient===
 
According to [[Thales|Thales of Miletus]], writing ''circa'' [[600 B.C.E.]], a form of electricity was known to the [[Ancient Greece|Ancient Greeks]], who found that rubbing [[fur]] on various substances, such as [[amber]], would cause a particular [[attraction]] between the two. The Greeks noted that the amber buttons could attract light objects such as [[hair]], and that if they rubbed the amber for long enough, they could even get a [[spark]] to jump. This is the origin of the word "electricity", from the [[Greek language|Greek]] ''&#275;lektron'' = "[[amber]]", which came from an old [[root (linguistics)|root]] ''&#275;lek-'' = "shine".
 
  
An object found in Iraq in [[1938]], dated to about [[250 B.C.E.]] and called the [[Baghdad Battery]], resembles a [[galvanic cell]] and is believed by some to have been used for [[electroplating]]. The conjecture that this or other ancient artifacts had an electrical function remains unproven, and such proposed ancient knowledge bears no known continuous relationship to the development of modern electrical technology.
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Gilbert was followed, in 1660, by [[Otto von Guericke]], who invented an early [[electrostatic]] generator. Other pioneers were [[Robert Boyle]], who in 1675, stated that electric attraction and repulsion can act across a vacuum; [[Stephen Gray (scientist)|Stephen Gray]], who in 1729, classified materials as [[conductor (material)|conductor]]s and [[Electrical insulation|insulator]]s; and [[C.F. Du Fay]], who first identified the two types of electricity that would later be called ''positive'' and ''negative''.
  
===Modern===
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The [[Leyden jar]], a type of [[capacitor]] for electrical energy in large quantities, was invented at Leiden University by Pieter van Musschenbroek in 1745. William Watson, experimenting with the Leyden jar, discovered in 1747, that a discharge of static electricity was equivalent to an [[electric current]].  
In [[1600]] the English scientist [[William Gilbert]] returned to the subject in ''De Magnete'', and coined the [[modern Latin]] word ''electricus'' from ''&eta;&lambda;&epsilon;&kappa;&tau;&rho;&omicron;&nu;'' (''elektron''), the Greek word for "amber", which soon gave rise to the English words ''electric'' and ''electricity''.  He was followed in [[1660]] by [[Otto von Guericke]], who is regarded as having invented an early electrostatic generator.  Other European pioneers were [[Robert Boyle]], who in [[1675]] stated that electric attraction and repulsion can act across a vacuum; [[Stephen Gray]], who in [[1729]] classified materials as [[conductor (material)|conductor]]s and [[insulator]]s; and [[C. F. Du Fay]], who first identified the two types of electricity that would later be called ''positive'' and ''negative''.  The [[Leyden jar]], a type of [[capacitor]] for electrical energy in large quantities, was invented at [[Leiden University]] by [[Pieter van Musschenbroek]] in [[1745]]. [[William Watson (scientist)|William Watson]], experimenting with the Leyden jar, discovered in [[1747]] that a discharge of static electricity was equivalent to an [[electric current]].
 
  
In [[June]], [[1752]], [[Benjamin Franklin]] promoted his investigations of electricity and theories through the famous, though extremely dangerous, [[experiment]] of flying a [[Kite flying|kite]] during a [[thunderstorm]]. Following these experiments he invented a [[lightning rod]] and established the link between [[lightning]] and electricity. If Franklin did fly a kite in a storm, he did not do it the way it is often described (as it would have been dramatic but fatal). It was either Franklin (more frequently) or [[Ebenezer Kinnersley]] of [[Philadelphia]] (less frequently) who created the convention of positive and negative electricity.
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In June 1752, [[Benjamin Franklin]] promoted his investigations of electricity and theories through the famous, though extremely dangerous, [[experiment]] of flying a kite during a [[thunderstorm]]. Following these experiments he invented a lightning rod and established the link between [[lightning]] and electricity. If Franklin did fly a kite in a storm, he did not do it the way it is often described (as it would have been dramatic, but fatal). It is either Franklin (more frequently) or Ebenezer Kinnersley of Philadelphia (less frequently) who is considered as responsible for establishing the convention of positive and negative electricity.
  
Franklin's observations aided later scientists such as [[Michael Faraday]], [[Luigi Galvani]], [[Alessandro Volta]], [[Andre Marie Ampere|André-Marie Ampère]], and [[Georg Ohm|Georg Simon Ohm]] whose work provided the basis for modern electrical technology. The work of Faraday, Volta, Ampere, and Ohm is honored by society, in that fundamental units of electrical measurement are named after them.
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Franklin's observations aided later scientists such as [[Michael Faraday]], [[Luigi Galvani]], [[Alessandro Volta]], [[André-Marie Ampère]], and [[Georg Ohm|Georg Simon Ohm]] whose work provided the basis for modern electrical technology. The work of Faraday, Volta, Ampère, and Ohm is honored by society, in that fundamental units of electrical measurement are named after them.  
  
Volta worked with [[chemicals]] and discovered that chemical reactions could be used to create positively charged [[anode]]s and negatively charged [[cathode]]s. When a conductor was attached between these, the [[voltage|difference in the electrical potential]] (also known as voltage) drives a [[current (electricity)|current]] between them through the conductor. The [[potential difference]] between two points is measured in units of [[volt]]s in recognition of Volta's work.  
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Volta discovered that [[chemical reaction]]s could be used to create positively charged [[anode]]s and negatively charged [[cathode]]s. When a conductor was attached between these, the [[voltage|difference in the electrical potential]] (also known as voltage) drove a [[current (electricity)|current]] between them through the conductor. The [[potential difference]] between two points is measured in units of [[volt]]s in recognition of Volta's work.  
  
The late 19th and early 20th century produced such giants of electrical engineering as [[Nikola Tesla]], inventor of the [[induction motor]] and the fundamental alternating current transmission system, [[Samuel Morse]], inventor of the telegraph; [[Antonio Meucci]], inventor of the telephone; [[Thomas Edison]] inventor of the [[phonograph]] and a practical [[incandescent light bulb]]; [[George Westinghouse]], inventor of the electric [[locomotive]]; [[Charles Steinmetz]], theoretician of alternating current.
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In 1800, Volta constructed the first device to produce a large electric current, later known as the [[battery (electricity)|electric battery]]. [[Napoleon Bonaparte|Napoleon]], informed of his works, summoned him in 1801, for a command performance of his experiments. He received many medals and decorations, including the Legion of Honor.
  
[[Nikola Tesla]] performed experiments with very high voltages that are the stuff of legend, involving [[ball lightning]] and other effects (some have been duplicated or explained; and others which have not). Nikola Tesla, inventor of the induction motor and developer of [[polyphase system]]s, contributed to the world of electrodynamics the theory of polyphase [[alternating current]], which he used to build the first induction motor, invented in [[1882]]. In May 1885, Westinghouse, then president of the Westinghouse Electric Company in [[Pittsburgh, Pennsylvania]], bought the rights to Tesla's patents for polyphase alternating-current dynamos. This led to a contest in the so-called [[court of public opinion]] as to which system would be adopted as the standard for power transmission (known as the [[War of Currents]]), Edison's direct-current system or Westinghouse's alternating-current method.  
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By the end of the nineteenth century, [[electrical engineering]] had become a distinct professional discipline and electrical engineers were considered separate from physicists and inventors. They created companies that investigated, developed and perfected the techniques of electricity transmission, and gained support from governments all over the world for starting the first worldwide electrical [[telecommunication]] network, the [[electric telegraph|telegraph network]]. Pioneers in this field included [[Werner von Siemens]], founder of Siemens AG in 1847, and John Pender, founder of Cable & Wireless.
  
Edison conducted a spirited [[public relations]] campaign which included his promotion of the [[electric chair]] as a method of [[execution (legal)|execution]]. The [[electric chair]] ran on Westinghouse's AC; Edison wanted to prove that AC power was capable of killing, and should therefore be viewed by the public as inherently dangerous. This [[FUD|fear, uncertainty and doubt]] campaign included the electrocution of [[Topsy the Elephant]].  AC power was eventually adopted as the standard.
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[[Image:PbsTesla.jpg|thumb|left|200px|Nikola Tesla]]
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The late nineteenth and early twentieth century produced such giants of electrical engineering as [[Nikola Tesla]], inventor of the polyphase [[induction motor]]; [[Samuel Morse]], inventor of a long-range telegraph; [[Antonio Meucci]], an inventor of the telephone; [[Thomas Edison]], inventor of the first commercial electrical energy distribution network; [[George Westinghouse]], inventor of the electric [[locomotive]]; [[Charles Steinmetz]], theoretician of alternating current; [[Alexander Graham Bell]], another inventor of the telephone and founder of a successful telephone business.  
  
== Electric power ==
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The rapid advance of electrical technology in the latter nineteenth and early twentieth centuries led to commercial rivalries, such as the so-called “War of the Currents” between Edison's direct-current (DC) system and Westinghouse's alternating-current (AC) method.
[[Image:Power pole.jpg|thumb|250px|An electric power pole]]
 
''See main article: [[Electric power]].''
 
  
"Electric power" is the popular name given to [[electrical energy]] production and distribution.   For most consumers, electrical energy is generated centrally by [[utility companies]] using [[coal]], [[natural gas]], [[hydropower]], [[nuclear power]] or [[petroleum]]. In 2000, U.S. electric utilities had 600 gigawatts of maximum summer generating capacity including 261 GW from coal, 118 GW from natural gas, 92 GW from hydropower, 86 GW from nuclear and 41 GW from petroleum.  Little generating capacity is presently based on [[renewable energy]] sources such as [[solar power]] and [[wind power]].  Some individuals and communities prefer renewable sources because there is less pollution and because users of renewable energy sources can sometimes gain a measure of economic independence from the electrical utilities.
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== Concepts in brief ==
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The term '''electricity''' involves several related concepts, defined below.
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* '''[[Electric charge]]:''' A fundamental conserved property of some [[subatomic particle]]s, which determines their [[electromagnetic interaction]]s. Electrically charged matter is influenced by, and produces, [[electromagnetic field]]s
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*'''[[Electric field]]:''' An effect produced by an electric charge that exerts a force on charged objects in its vicinity
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*'''[[Electric current]]:''' A movement or flow of electrically charged particles
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*'''[[Electric potential]]''' (often called ''[[voltage]]''): The potential energy per unit charge associated with a static electric field
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*'''[[Electrical resistance]]:''' A measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the [[ohm (unit)|ohm]]
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*'''[[Electrical conductance]]:''' The reciprocal of electrical resistance, it is measured in [[Siemens (unit)|siemens]]
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*'''[[Electrical energy]]:''' The energy made available by the flow of electric charge through an [[electrical conductor]]
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*'''[[Electric power]]:''' The rate at which electric energy is converted to or from another energy form, such as light, heat, or mechanical energy
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*'''[[Electric conductor]]:''' Any material that easily permits the flow of electric current
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*'''[[electric insulator]]:''' Any material that inhibits the flow of electric current
  
Devices powered by electrical energy include lamps, [[computer]]s and the [[Internet]], [[radio]] and [[television]], [[refrigeration]], [[air conditioning]], [[traffic signal]]s, [[electric guitar]]s and other [[electronic music|electronic musical instrument]]s, and the [[spark plug]]s in [[automobile]]s. A summary of the applications of electric energy (written for non-specialists, and briefly explaining motors, transformers, transistors, digital, etc.) is the book, ''Industrial Electronics for Engineers, Chemists, and Technicians'', by D. J. Shanefield, William Andrew Publishing (Norwich, NY), 2001.
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== Concepts in detail ==
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=== Electric charge ===
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Electric charge is a property of certain [[subatomic particle]]s (for example, [[electron]]s and [[proton]]s) which interacts with [[electromagnetic fields]] and causes attractive and repulsive [[force]]s between them.
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Electric charge gives rise to one of the four [[fundamental force]]s of nature, and is a conserved property of [[matter]] that can be quantified. In this sense, the phrase "[[quantity of electricity]]" is used interchangeably with the phrases "[[electric charge|charge of electricity]]" and "[[quantity of charge]]." There are two types of charge: Positive and negative. Through experimentation, one finds that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by [[Coulomb's law]].
  
=== Safety in power systems ===
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=== Electric field ===
It is often important that one side of a circuit be electrically bonded to an earth terminal. Such an earth terminal is usually connected to an electrode buried in the ground. The potential of earth (ground) is defined as zero by convention, and the electrical resistance between similarly buried electrodes is usually low enough that all earth terminals within a given area can be considered to be at the same voltage.
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[[Image:Faraday.jpg|thumb|200px|Michael Faraday]]
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The space surrounding an electric charge has a property called an electric field. This electric field exerts a force on other electrically charged objects. The concept of electric fields was introduced by [[Michael Faraday]].
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[[Image:Efield.png|thumb|left|200px|Illustration of the electric vector field surrounding two opposite point charges. Red is positive, green is negative.]]
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An electric field is a vector with SI units of newtons per coulomb (N C<sup>-1</sup>) or, equivalently, [[volt]]s per meter (V m<sup>-1</sup>). The direction of the field at a point is defined by the direction of the electric force exerted on a positive test charge placed at that point. The strength of the field is defined by the ratio of the electric force on a charge at a point to the magnitude of the charge placed at that point. Electric fields contain electrical energy with energy density proportional to the square of the field intensity. The electric field is to charge as acceleration is to mass and force density is to volume.
  
=== Applications ===
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The electrical field force acts between two charges, in the same way that the [[gravitational field]] force acts between two [[mass]]es. However, the electric field is a little bit different. Gravitational force depends on the masses of two bodies, whereas electric force depends on the magnitude of electric charges of two bodies. While gravity can only pull two masses together, the electric force can be an attractive ''or'' repulsive force. If both charges are of same sign (for example, both positive), there will be a repulsive force between the two. If the charges are opposite, there will be an attractive force between the two bodies. The magnitude of the force varies inversely with the square of the distance between the two bodies, and is also proportional to the product of the unsigned magnitudes of the two charges.
  
In [[electrical engineering]], the energy in electromagnetic fields is harnessed to perform useful work&mdash;either as a method to transmit energy to the appropriate place and then convert it back into a different, useful form of energy (for instance, heat, light, or motion), or by using the presence or level of electricity to convey [[information]].
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=== Electric potential (voltage) ===
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[[Image:High voltage warning.svg|right|thumb|International safety symbol "Caution, risk of electric shock" (ISO 3864), colloquially known as the ''high voltage symbol'']]
  
===Producing electrical energy===
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The difference in electric potential between two points is called '''[[voltage]].''' It is a measure of the capacity of an [[electric field]] to cause an [[electric current]] to flow through an [[electrical conductor]].
''See also: [[Electricity generation]]''
 
  
There are many different types of [[Generator|generators]] to produce electrical energy: Hydropower, nuclear power, solar power, and wind power. These different types of generators use different natural and man-made materials to liberate energy.  
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The difference in electric potential is defined as the [[Mechanical work|work]] done per unit charge (against electrical forces) in moving a positive point charge slowly between two points. If one of the points is taken to be a reference point with zero potential, then the electric potential at any point can be defined in terms of the work done per unit charge in moving a positive point charge from that reference point to the point at which the potential is to be determined. For isolated charges, the reference point is usually taken to be [[infinity]]. Voltage is measured in [[volts]] (1 volt = 1 [[joule]]/[[coulomb]]).
  
====Hydropower====
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The electric potential is analogous to [[temperature]]: There is a different temperature at every point in space, and the [[temperature gradient]] indicates the direction and magnitude of the driving force behind heat flow. Similarly, there is an electric potential at every point in space, and its [[gradient]] indicates the direction and magnitude of the driving force behind charge movement.
''See main article: [[Hydropower]]''
 
  
Hydropower consists in taking advantage of water falling or flowing, most of the time at waterfalls or rivers, to convert the mechanical energy into electrical energy by using generators coupled to turbines.
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=== Electric current ===
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An [[electric current]] is a flow of [[electric charge]] and is measured in [[ampere]]s. Examples of electric currents include metallic conduction, where [[electron]]s flow through a [[Electrical conductor|conductor or conductors]] such as a metal [[wire]], and [[electrolysis]], where [[ion]]s (charged [[atom]]s) flow through liquids. The particles themselves often move quite slowly, while the [[electric field]] that drives them propagates at close to the [[speed of light]].
  
====Nuclear power====
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A [[direct current]] (DC) is a unidirectional flow, while an [[alternating current]] (AC) reverses direction repeatedly. The time average of an alternating current is zero, but its energy capability ([[root mean square|RMS]] value) is not zero.
''See main article: [[nuclear power]]''
 
  
Nuclear power uses heat generated by [[nuclear fission]] of either [[uranium]] or [[plutonium]] to heat a liquid, usually water. This heat then drives a [[steam engine]] to turn a generator and produce electrical energy. Nuclear [[fusion]] generates greater energy than fission. However, a convenient and cheaper way of harnessing fusion is still being researched.
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[[#Ohm's law|Ohm's law]] is an important relationship describing the behavior of electric currents, relating them to [[voltage]].
  
====Solar power====
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For historical reasons, electric [[Current (electricity)|current]] is said to flow from the most positive part of a circuit to the most negative part. The electric current thus defined is called ''[[conventional current]]''. It is now known that, depending on the conditions, an electric current can consist of a flow of charged particles in either direction or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation. However, if another definition is used&mdash;for example, "electron current"&mdash;it should be explicitly stated.
''See main article: [[Solar power]]''
 
Solar power is created by the sun's radiant energy falling on the earth. The energy from the sun excites electrons in a semiconductor material which gives rise to a photo voltaic potential.
 
  
====Wind power====
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=== Electrical resistance ===
''See main article: [[wind power]]''
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Electrical resistance represents the degree to which a device in an electric circuit opposes the passage of an [[electric current]]. For any given voltage applied to an electric circuit, the quantity of resistance in the circuit determines the amount of current flowing through the circuit. The relationship between voltage, current, and resistance in an electric circuit can be written as an equation known as [[#Ohm's law|Ohm's law]], given below.
  
Energy is captured from the wind by the use of [[wind turbine]]s. The most common type of wind turbine is three-bladed, though two- and four-bladed ones can be found. Most turbines have blades that rotate perpendicular to the wind, though there is a variety that rotates parallel to it.
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For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied [[voltage]].
  
Wind turbines must be placed in an area where there is an almost constant source of wind. The most productive locations are on or near the shore of a large lake, sea or ocean, though they can be placed anywhere that there is a breeze.
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Its [[reciprocal]] quantity of electrical resistance is [[electrical conductance]]. The [[SI]] unit of electrical resistance is the [[ohm (unit)|ohm]].
  
====Burning of fuel====
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=== Electrical energy ===
''See main article: [[Fossil fuel power plant]]''
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Electrical energy is energy stored in an [[electric field]] or transported by an [[electric current]]. Energy is defined as the ability to do [[work (physics)|work]], and electrical energy is simply one of the many types of energy. Examples of electrical energy include:
  
Energy is captured from the heat given off by coal, oil, wood and fossil fuels. These are often used when no other means of energy generation can be used, either because of the local geography or technical issues. It is also one of the worst [[pollution|polluting]] type of generator.
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* The energy that is constantly stored in the Earth's [[atmosphere]], and is partly released during a [[thunderstorm]] in the form of [[lightning]]
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* The energy that is stored in the coils of an [[electrical generator]] in a [[power station]], and is then transmitted by wires to the consumer; the consumer then pays for each unit of energy received
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* The energy that is stored in a [[capacitor]], and can be released to drive a current through an [[electrical circuit]]
  
== Electric current ==
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=== Electric power ===
The electric charge which occurs naturally within [[Conductor (material)|conductor]]s can be forced to flow, while the charges within [[insulator]]s are locked in place and cannot be moved. Devices that use charge flow principles in materials are called [[electronics|electronic devices]]. A flow of electric charge is called an [[current (electricity)|electric current]]. 
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Electric power is the rate at which electrical energy is produced or consumed, and is measured in [[watt]]s (W).  
A [[direct current]] (DC) is a unidirectional flow; [[alternating current]] (AC) is a flow whose time average is zero, but whose energy capability ([[RMS]] level) is  not zero.  With AC the electric current repeatedly changes [[direction]].  
 
  
See [[electrical conduction]]
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A [[fossil fuel|fossil-fuel]] or [[nuclear power|nuclear]] [[power station]] converts heat to electrical energy, and the faster the station burns fuel, assuming constant efficiency of conversion, the higher its power output. The output of a power station is usually specified in megawatts (millions of watts). The electrical energy is then sent over [[transmission line]]s to reach the consumers.
  
[[Ohm's Law]] is an important relationship describing the behaviour of electric currents:
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Every consumer uses appliances that convert the electrical energy to other forms of energy, such as [[heat]] (in [[electric arc furnace]]s and [[electric heater]]s), [[light]] (in [[light bulb]]s and [[fluorescent lamp]]s), or motion, that is, [[kinetic energy]] (in [[electric motor]]s). Like the power station, each appliance is also rated in watts, depending on the rate at which it converts electrical energy into another form. The power station must produce electrical energy at the same rate as all the connected appliances consume it.
  
:<math>V = I \cdot R \,</math>
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Non-nuclear electric power is categorized as either green or brown electricity. Green power is a cleaner alternative energy source in comparison to traditional sources, and is derived from renewable energy resources that do not produce any nuclear waste; examples include energy produced from wind, water, solar, thermal, hydro, combustible renewables and waste. Electricity from coal, oil, and natural gas is known as traditional power or "brown" electricity.
  
where
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== Ohm's law ==
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[[Image:Ohms law voltage source2.svg.png|right|thumb|250px|A voltage source, ''V,'' drives an electric current, ''I,'' through resistor, ''R''. The three quantities obey Ohm's law: V = IR]]
  
<math>V</math> is the applied voltage, measured in [[volt]]s
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'''Ohm's law''' states that in an [[electrical circuit]], the [[electric current|current]] passing through a conductor, from one terminal point on the conductor to another, is directly [[Proportionality (mathematics)|proportional]] to the [[potential difference]] (that is, [[voltage drop]] or [[voltage]]) across the two terminal points and inversely proportional to the resistance of the conductor between the two points.
  
<math>I</math> is the current, measured in [[ampere]]s
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In mathematical terms, this is written as:
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:<math>I = \frac VR</math>
  
<math>R</math> is the resistance, measured in [[ohm]]s
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where ''I'' is the current, ''V'' is the potential difference, and ''R'' is a constant called the [[electrical resistance|resistance]]. The potential difference is also known as the [[voltage drop]], and is sometimes denoted by ''E'' instead of ''V''. This law is usually valid over a large range of values of current and voltage, but it breaks down if conditions (such as temperature) are changed excessively.
  
For historical reasons, electric [[current]] is said to flow from the most positive part of a circuit to the most negative part. The electric current thus defined is called ''[[conventional current]]''. It is now known that, depending on the type of conductor, an electric current can consist of a flow of charged particles in either direction, or even in both directions at once.  The positive-to-negative convention is widely used to simplify this situation.  If another definition is used - for example, "electron current" - it should be explicitly stated.
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The SI unit of current is the [[ampere]]; that of potential difference is the [[volt]]; and that of resistance is the [[ohm (unit)|ohm]]. One ohm is equal to one volt per ampere. The law is named after the physicist [[Georg Ohm]], who published it in a slightly more complex form in 1826. The above equation could not exist until the [[ohm]], a unit of resistance, was defined (1861, 1864).
  
== SI electricity units ==
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== Electrical phenomena in nature ==
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* [[Matter]]: [[Atom]]s and [[molecule]]s are held together by electric forces between charged particles.
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* [[Lightning]]: Electrical discharges in the atmosphere.
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* The [[Earth's magnetic field]]: Created by electric currents circulating in the planet's core.
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* Sometimes due to [[solar flare]]s, a phenomenon known as a [[power surge]] can be created.
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*[[Piezoelectricity]]: The ability of certain crystals to generate a voltage in response to applied mechanical stress.
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*[[triboelectric effect|Triboelectricity]]: Electric charge taken on by contact or friction between two different materials.
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* [[Bioelectromagnetism]]: Electrical phenomena within living organisms.
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** [[Bioelectricity]]: Many animals are sensitive to electric fields, some (such as [[shark]]s) more than others (such as people). Most also generate their own electric fields.
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*** [[Gymnotiformes]], such as the [[electric eel]], deliberately generate strong fields to detect or stun their prey.
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*** [[Neuron]]s in the [[nervous system]] transmit information by electrical impulses known as [[action potential]]s.
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== Uses of electricity ==
 +
Electricity is used in many of our appliances machines and tools today. Examples include in lighting, communications, industrial machinery, power tools, vehicles, computers, appliances, elevators and many other electronic goods. Electricity is so widely used because of its relative ease of transmission and the ease with which the energy it carries can be harnessed to do useful work.
 +
 
 +
== SI units for electricity and magnetism ==
 
{{SI_electromagnetism_units}}
 
{{SI_electromagnetism_units}}
  
 
== See also ==
 
== See also ==
* '''Main''': [[electromagnetism|electromagnetic]], [[electrical phenomenon|phenomenon]] ([[electric charge]]), [[electric power]] (for energy transfer using electricity), [[electric shock]], [[electric chair]] (execution)
+
* [[Electromagnetism]]
* '''Things''': [[Battery (electricity)|Battery]], [[Lightning]], [[Conductor (material)|Conductor]], [[Insulator|Insulator]], [[Leyden jar]]
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* [[Electrical engineering]]
* '''Engineering''': [[Green electricity]], [[Electrical wiring]]
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* [[Electronics]]
* '''Safety''': [[High-voltage hazards]]
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* [[Electrostatics]]
 +
* [[Battery (electricity)]]
 +
* [[Insulator]]
 +
* [[Electrical conductor]]
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* [[Capacitor]]
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* [[Inductor]]
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* [[Electric motor]]
  
=== Electrical phenomena in nature ===
+
==Notes==
* [[Lightning]]
+
<references/>
* [[Bioelectricity]] &mdash; Many animals are sensitive to electric fields, some (e.g., [[shark]]s) more than others (e.g., people). Most also generate their own electric fields.
+
 
* [[Gymnotiformes]], such as the [[electric eel]], deliberately generate strong fields to detect or stun their prey.
+
==References==
* [[Neuron]]s in the [[nervous system]] transmit information by electrical impulses known as [[action potential]]s.
+
 
* [[Matter]] &mdash; since [[atom]]s and [[molecule]]s are held together by electric forces.
+
* Callister, William D. 2006. ''Materials Science and Engineering: An Introduction.'' New York: Wiley and Sons. ISBN 0471736961.
* The [[Earth's magnetic field]] &mdash; created by electric currents circulating in the planet's core.
+
* Gibilisco, Stan. 2005. ''Electricity Demystified.'' New York: McGraw-Hill. ISBN 0071439250.
* Sometimes due to [[solar flare]]s, a phenomenon known as a [[power surge]] can be created, which can be very damaging to sensitive electrical equipment such as [[computer]]s. However, such damage can be prevented by using a [[surge protector]].
+
* Saslow, Wayne, and Lane H. Seeley. 2006. Electricity, Magnetism and Light. ''American Journal of Physics'' 74 (4): 365.
 +
* Young, Hugh D., and Roger A. Freedman. 2003. ''Physics for Scientists and Engineers,'' 11th edition. San Francisco: Pearson. ISBN 080538684X.
  
 
== External links ==  
 
== External links ==  
* [http://amasci.com/miscon/whatis.html  What is electricity?]
+
All links retrieved September 16, 2013.
* [http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=electricity Merriam-Webster: Electricity]
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* [http://www.bibliomania.com/2/9/72/119/21387/1.html Tyndall: Faraday as Discovery: Identity of Electricities]
+
* [http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=electricity Merriam-Webster: Electricity]  
* [http://www.eia.doe.gov/fuelelectric.html US Energy Department Statistics]
+
* [http://www.bibliomania.com/2/9/72/119/21387/1.html Tyndall: Faraday as Discovery: Identity of Electricities]  
* [http://www.mouthshut.com/readreview/38842-1.html How to save on your electricity bills]
+
* [http://www.worldstandards.eu/electricity.htm Electricity around the world]  
* [http://users.pandora.be/worldstandards/electricity.htm Electricity around the world]
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* [http://www.micro.magnet.fsu.edu/electromag/index.html Electricity and Magnetism]  
* [http://www.tufts.edu/as/wright_center/fellows/bob_morse_04/ A Comprehensive Collection of Franklin’s Electrical Works: The Electrical Writings of Benjamin Franklin], Created and Collected by Robert A. Morse (2004)
 
  
[[Category:Electricity|*]]
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[[Category:Physical sciences]]
[[Category:Physical_sciences]]
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[[Category:Physics]]
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[[Category:Electromagnetism]]
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[[Category:Electrical engineering]]
  
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Revision as of 15:38, 16 September 2013


Electromagnetism
Solenoid.svg
Electricity ·Magnetism

Electricity (from Greek ήλεκτρον (electron) "amber") is a general term for the variety of phenomena resulting from the presence and flow of electric charge. Together with magnetism, it constitutes the fundamental interaction known as electromagnetism. It includes several well-known physical phenomena, such as lightning, electric fields, and electric currents. Electricity requires setting up a circuit between positively charged and negatively charged poles. As such, it is a prime example of a general principle that energy of any kind is predicated upon the relationship between subject and object entities.

Human ability to harness electricity is one of the keys for the establishment of modern technological society. Thus, electricity is used for lighting, communications, transportation, industrial machinery, power tools, appliances, elevators, computers, and an expanding variety of electronic goods.

Lightning strikes during a night-time thunderstorm. As powerful electric currents flow through the Earth's atmosphere, energy is radiated as light.

History of electricity

The ancient Greeks and Parthians knew of static electricity from rubbing objects against fur. The ancient Babylonians may have had some knowledge of electroplating, based on the discovery of the Baghdad Battery,[1] which resembles a Galvanic cell.

Franklin kite plaque at Saint Stephen's Church, Philadelphia

It was Italian physician Girolamo Cardano in De Subtilitate (1550) who is credited with distinguishing, perhaps for the first time, between electrical and magnetic forces. In 1600, the English scientist William Gilbert, in De Magnete, expanded on Cardano's work and coined the New Latin word electricus from ἤλεκτρον (elektron), the Greek word for "amber." The first usage of the word electricity is ascribed to Sir Thomas Browne in his 1646 work, Pseudodoxia Epidemica.

Gilbert was followed, in 1660, by Otto von Guericke, who invented an early electrostatic generator. Other pioneers were Robert Boyle, who in 1675, stated that electric attraction and repulsion can act across a vacuum; Stephen Gray, who in 1729, classified materials as conductors and insulators; and C.F. Du Fay, who first identified the two types of electricity that would later be called positive and negative.

The Leyden jar, a type of capacitor for electrical energy in large quantities, was invented at Leiden University by Pieter van Musschenbroek in 1745. William Watson, experimenting with the Leyden jar, discovered in 1747, that a discharge of static electricity was equivalent to an electric current.

In June 1752, Benjamin Franklin promoted his investigations of electricity and theories through the famous, though extremely dangerous, experiment of flying a kite during a thunderstorm. Following these experiments he invented a lightning rod and established the link between lightning and electricity. If Franklin did fly a kite in a storm, he did not do it the way it is often described (as it would have been dramatic, but fatal). It is either Franklin (more frequently) or Ebenezer Kinnersley of Philadelphia (less frequently) who is considered as responsible for establishing the convention of positive and negative electricity.

Franklin's observations aided later scientists such as Michael Faraday, Luigi Galvani, Alessandro Volta, André-Marie Ampère, and Georg Simon Ohm whose work provided the basis for modern electrical technology. The work of Faraday, Volta, Ampère, and Ohm is honored by society, in that fundamental units of electrical measurement are named after them.

Volta discovered that chemical reactions could be used to create positively charged anodes and negatively charged cathodes. When a conductor was attached between these, the difference in the electrical potential (also known as voltage) drove a current between them through the conductor. The potential difference between two points is measured in units of volts in recognition of Volta's work.

In 1800, Volta constructed the first device to produce a large electric current, later known as the electric battery. Napoleon, informed of his works, summoned him in 1801, for a command performance of his experiments. He received many medals and decorations, including the Legion of Honor.

By the end of the nineteenth century, electrical engineering had become a distinct professional discipline and electrical engineers were considered separate from physicists and inventors. They created companies that investigated, developed and perfected the techniques of electricity transmission, and gained support from governments all over the world for starting the first worldwide electrical telecommunication network, the telegraph network. Pioneers in this field included Werner von Siemens, founder of Siemens AG in 1847, and John Pender, founder of Cable & Wireless.

File:PbsTesla.jpg
Nikola Tesla

The late nineteenth and early twentieth century produced such giants of electrical engineering as Nikola Tesla, inventor of the polyphase induction motor; Samuel Morse, inventor of a long-range telegraph; Antonio Meucci, an inventor of the telephone; Thomas Edison, inventor of the first commercial electrical energy distribution network; George Westinghouse, inventor of the electric locomotive; Charles Steinmetz, theoretician of alternating current; Alexander Graham Bell, another inventor of the telephone and founder of a successful telephone business.

The rapid advance of electrical technology in the latter nineteenth and early twentieth centuries led to commercial rivalries, such as the so-called “War of the Currents” between Edison's direct-current (DC) system and Westinghouse's alternating-current (AC) method.

Concepts in brief

The term electricity involves several related concepts, defined below.

  • Electric charge: A fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields
  • Electric field: An effect produced by an electric charge that exerts a force on charged objects in its vicinity
  • Electric current: A movement or flow of electrically charged particles
  • Electric potential (often called voltage): The potential energy per unit charge associated with a static electric field
  • Electrical resistance: A measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the ohm
  • Electrical conductance: The reciprocal of electrical resistance, it is measured in siemens
  • Electrical energy: The energy made available by the flow of electric charge through an electrical conductor
  • Electric power: The rate at which electric energy is converted to or from another energy form, such as light, heat, or mechanical energy
  • Electric conductor: Any material that easily permits the flow of electric current
  • electric insulator: Any material that inhibits the flow of electric current

Concepts in detail

Electric charge

Electric charge is a property of certain subatomic particles (for example, electrons and protons) which interacts with electromagnetic fields and causes attractive and repulsive forces between them. Electric charge gives rise to one of the four fundamental forces of nature, and is a conserved property of matter that can be quantified. In this sense, the phrase "quantity of electricity" is used interchangeably with the phrases "charge of electricity" and "quantity of charge." There are two types of charge: Positive and negative. Through experimentation, one finds that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by Coulomb's law.

Electric field

Michael Faraday

The space surrounding an electric charge has a property called an electric field. This electric field exerts a force on other electrically charged objects. The concept of electric fields was introduced by Michael Faraday.

File:Efield.png
Illustration of the electric vector field surrounding two opposite point charges. Red is positive, green is negative.

An electric field is a vector with SI units of newtons per coulomb (N C-1) or, equivalently, volts per meter (V m-1). The direction of the field at a point is defined by the direction of the electric force exerted on a positive test charge placed at that point. The strength of the field is defined by the ratio of the electric force on a charge at a point to the magnitude of the charge placed at that point. Electric fields contain electrical energy with energy density proportional to the square of the field intensity. The electric field is to charge as acceleration is to mass and force density is to volume.

The electrical field force acts between two charges, in the same way that the gravitational field force acts between two masses. However, the electric field is a little bit different. Gravitational force depends on the masses of two bodies, whereas electric force depends on the magnitude of electric charges of two bodies. While gravity can only pull two masses together, the electric force can be an attractive or repulsive force. If both charges are of same sign (for example, both positive), there will be a repulsive force between the two. If the charges are opposite, there will be an attractive force between the two bodies. The magnitude of the force varies inversely with the square of the distance between the two bodies, and is also proportional to the product of the unsigned magnitudes of the two charges.

Electric potential (voltage)

International safety symbol "Caution, risk of electric shock" (ISO 3864), colloquially known as the high voltage symbol

The difference in electric potential between two points is called voltage. It is a measure of the capacity of an electric field to cause an electric current to flow through an electrical conductor.

The difference in electric potential is defined as the work done per unit charge (against electrical forces) in moving a positive point charge slowly between two points. If one of the points is taken to be a reference point with zero potential, then the electric potential at any point can be defined in terms of the work done per unit charge in moving a positive point charge from that reference point to the point at which the potential is to be determined. For isolated charges, the reference point is usually taken to be infinity. Voltage is measured in volts (1 volt = 1 joule/coulomb).

The electric potential is analogous to temperature: There is a different temperature at every point in space, and the temperature gradient indicates the direction and magnitude of the driving force behind heat flow. Similarly, there is an electric potential at every point in space, and its gradient indicates the direction and magnitude of the driving force behind charge movement.

Electric current

An electric current is a flow of electric charge and is measured in amperes. Examples of electric currents include metallic conduction, where electrons flow through a conductor or conductors such as a metal wire, and electrolysis, where ions (charged atoms) flow through liquids. The particles themselves often move quite slowly, while the electric field that drives them propagates at close to the speed of light.

A direct current (DC) is a unidirectional flow, while an alternating current (AC) reverses direction repeatedly. The time average of an alternating current is zero, but its energy capability (RMS value) is not zero.

Ohm's law is an important relationship describing the behavior of electric currents, relating them to voltage.

For historical reasons, electric current is said to flow from the most positive part of a circuit to the most negative part. The electric current thus defined is called conventional current. It is now known that, depending on the conditions, an electric current can consist of a flow of charged particles in either direction or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation. However, if another definition is used—for example, "electron current"—it should be explicitly stated.

Electrical resistance

Electrical resistance represents the degree to which a device in an electric circuit opposes the passage of an electric current. For any given voltage applied to an electric circuit, the quantity of resistance in the circuit determines the amount of current flowing through the circuit. The relationship between voltage, current, and resistance in an electric circuit can be written as an equation known as Ohm's law, given below.

For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied voltage.

Its reciprocal quantity of electrical resistance is electrical conductance. The SI unit of electrical resistance is the ohm.

Electrical energy

Electrical energy is energy stored in an electric field or transported by an electric current. Energy is defined as the ability to do work, and electrical energy is simply one of the many types of energy. Examples of electrical energy include:

  • The energy that is constantly stored in the Earth's atmosphere, and is partly released during a thunderstorm in the form of lightning
  • The energy that is stored in the coils of an electrical generator in a power station, and is then transmitted by wires to the consumer; the consumer then pays for each unit of energy received
  • The energy that is stored in a capacitor, and can be released to drive a current through an electrical circuit

Electric power

Electric power is the rate at which electrical energy is produced or consumed, and is measured in watts (W).

A fossil-fuel or nuclear power station converts heat to electrical energy, and the faster the station burns fuel, assuming constant efficiency of conversion, the higher its power output. The output of a power station is usually specified in megawatts (millions of watts). The electrical energy is then sent over transmission lines to reach the consumers.

Every consumer uses appliances that convert the electrical energy to other forms of energy, such as heat (in electric arc furnaces and electric heaters), light (in light bulbs and fluorescent lamps), or motion, that is, kinetic energy (in electric motors). Like the power station, each appliance is also rated in watts, depending on the rate at which it converts electrical energy into another form. The power station must produce electrical energy at the same rate as all the connected appliances consume it.

Non-nuclear electric power is categorized as either green or brown electricity. Green power is a cleaner alternative energy source in comparison to traditional sources, and is derived from renewable energy resources that do not produce any nuclear waste; examples include energy produced from wind, water, solar, thermal, hydro, combustible renewables and waste. Electricity from coal, oil, and natural gas is known as traditional power or "brown" electricity.

Ohm's law

File:Ohms law voltage source2.svg.png
A voltage source, V, drives an electric current, I, through resistor, R. The three quantities obey Ohm's law: V = IR

Ohm's law states that in an electrical circuit, the current passing through a conductor, from one terminal point on the conductor to another, is directly proportional to the potential difference (that is, voltage drop or voltage) across the two terminal points and inversely proportional to the resistance of the conductor between the two points.

In mathematical terms, this is written as:

where I is the current, V is the potential difference, and R is a constant called the resistance. The potential difference is also known as the voltage drop, and is sometimes denoted by E instead of V. This law is usually valid over a large range of values of current and voltage, but it breaks down if conditions (such as temperature) are changed excessively.

The SI unit of current is the ampere; that of potential difference is the volt; and that of resistance is the ohm. One ohm is equal to one volt per ampere. The law is named after the physicist Georg Ohm, who published it in a slightly more complex form in 1826. The above equation could not exist until the ohm, a unit of resistance, was defined (1861, 1864).

Electrical phenomena in nature

  • Matter: Atoms and molecules are held together by electric forces between charged particles.
  • Lightning: Electrical discharges in the atmosphere.
  • The Earth's magnetic field: Created by electric currents circulating in the planet's core.
  • Sometimes due to solar flares, a phenomenon known as a power surge can be created.
  • Piezoelectricity: The ability of certain crystals to generate a voltage in response to applied mechanical stress.
  • Triboelectricity: Electric charge taken on by contact or friction between two different materials.
  • Bioelectromagnetism: Electrical phenomena within living organisms.
    • Bioelectricity: Many animals are sensitive to electric fields, some (such as sharks) more than others (such as people). Most also generate their own electric fields.
      • Gymnotiformes, such as the electric eel, deliberately generate strong fields to detect or stun their prey.
      • Neurons in the nervous system transmit information by electrical impulses known as action potentials.

Uses of electricity

Electricity is used in many of our appliances machines and tools today. Examples include in lighting, communications, industrial machinery, power tools, vehicles, computers, appliances, elevators and many other electronic goods. Electricity is so widely used because of its relative ease of transmission and the ease with which the energy it carries can be harnessed to do useful work.

SI units for electricity and magnetism

SI electromagnetism units
Symbol Name of Quantity Derived Units Unit Base Units
I Current ampere (SI base unit) A A = W/V = C/s
q Electric charge, Quantity of electricity coulomb C A·s
V Potential difference volt V J/C = kg·m2·s−3·A−1
R, Z, X Resistance, Impedance, Reactance ohm Ω V/A = kg·m2·s−3·A−2
ρ Resistivity ohm metre Ω·m kg·m3·s−3·A−2
P Power, Electrical watt W V·A = kg·m2·s−3
C Capacitance farad F C/V = kg−1·m−2·A2·s4
Elastance reciprocal farad F−1 V/C = kg·m2·A−2·s−4
ε Permittivity farad per metre F/m kg−1·m−3·A2·s4
χe Electric susceptibility (dimensionless) - -
G, Y, B Conductance, Admittance, Susceptance siemens S Ω−1 = kg−1·m−2·s3·A2
σ Conductivity siemens per metre S/m kg−1·m−3·s3·A2
H Auxiliary magnetic field, magnetic field intensity ampere per metre A/m A·m−1
Φm Magnetic flux weber Wb V·s = kg·m2·s−2·A−1
B Magnetic field, magnetic flux density, magnetic induction, magnetic field strength tesla T Wb/m2 = kg·s−2·A−1
Reluctance ampere-turns per weber A/Wb kg−1·m−2·s2·A2
L Inductance henry H Wb/A = V·s/A = kg·m2·s−2·A−2
μ Permeability henry per metre H/m kg·m·s−2·A−2
χm Magnetic susceptibility (dimensionless) - -

See also

Notes

  1. BBC News, Riddle of 'Baghdad's batteries.’ Retrieved June 27, 2007.

References
ISBN links support NWE through referral fees

  • Callister, William D. 2006. Materials Science and Engineering: An Introduction. New York: Wiley and Sons. ISBN 0471736961.
  • Gibilisco, Stan. 2005. Electricity Demystified. New York: McGraw-Hill. ISBN 0071439250.
  • Saslow, Wayne, and Lane H. Seeley. 2006. Electricity, Magnetism and Light. American Journal of Physics 74 (4): 365.
  • Young, Hugh D., and Roger A. Freedman. 2003. Physics for Scientists and Engineers, 11th edition. San Francisco: Pearson. ISBN 080538684X.

External links

All links retrieved September 16, 2013.

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