Difference between revisions of "Electricity" - New World Encyclopedia

From New World Encyclopedia
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:''Separate-but related articles are [[Electrical energy]], and [[Electric power]]''
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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.]]
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{{electromagnetism}}
  
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''''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 many well-known [[physics|physical]] phenomena such as [[lightning]], [[electric field]]s, and [[electric current]]s, and is put to use in [[Industry|industrial]] applications such as [[electronics]] and [[electric power]].  
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[[image:Lightning.jpg|250px|thumb|right|[[Lightning]] strikes during a night-time thunderstorm.]]
 
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== Electric charge ==
 
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[[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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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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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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==Concepts in electricity==
  
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== History ==
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In casual usage, the term '''electricity''' is applied to several related concepts that are better identified by more precise terms:
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===Ancient===
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*'''[[Electric potential]]'''  (often referred to as '''[[voltage]])''' - the potential energy per unit charge associated with a static electric field.
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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]] ''ēlektron'' = "[[amber]]", which came from an old [[root (linguistics)|root]] ''ēlek-'' = "shine".
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*'''[[Electric current]]''' - a movement or flow of electrically charged particles.
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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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*'''[[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 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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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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A spark of static electricity can measure up to three thousand (3,000) [[volts.]]
  
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===Modern===
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== History of discovery ==
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In [[1600]] the English scientist [[William Gilbert]] returned to the subject in ''De Magnete'', and coined the [[modern Latin]] word ''electricus'' from ''ηλεκτρον'' (''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]].
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{{main|History of 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 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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The ancient [[Ancient Greece|Greeks]] and [[Parthia]]ns knew of static electricity from rubbing objects against fur. The ancient [[Babylonia]]ns may have had some knowledge of [[electroplating]], based on the discovery of the [[Baghdad Battery]], which resmbles a [[Galvanic cell]].
  
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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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[[Image:Saint Stephen's church plaque.png|thumb|left|Franklin kite plaque at Saint Stephen's Church, Philadelphia.]]
  
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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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Though [[Benjamin Franklin]]'s famous "invention" of electricity by flying a kite in a thunderstorm turned out to be more fiction than fact, his theories on the relationship between lightning and static electricity sparked the interest of later scientists whose work provided the basis for modern electrical technology. Most notably these include [[Luigi Galvani]] (1737–1798), [[Alessandro Volta]] (1745-1827), [[Michael Faraday]] (1791–1867), [[Andre Marie Ampere|André-Marie Ampère]] (1775–1836), and [[Georg Ohm|Georg Simon Ohm]] (1789-1854). The late 19th and early 20th century produced such giants of electrical engineering as [[Nikola Tesla]], [[Samuel Morse]], [[Antonio Meucci]], [[Thomas Edison]], [[George Westinghouse]], [[Werner von Siemens]], [[Charles Steinmetz]], and [[Alexander Graham Bell]].
  
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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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[[Image:PbsTesla.jpg|thumb|right|200px|Nikola Tesla.]]
  
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[[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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== Concepts in detail ==
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=== Electric charge ===
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{{Main|Electric charge}}
  
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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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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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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: 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]].
  
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== Electric power ==
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=== Electric field ===
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[[Image:Power pole.jpg|thumb|250px|An electric power pole]]
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{{Main|Electric field}}
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''See main article: [[Electric power]].''
 
  
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"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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[[Image:Faraday.jpg|thumb|left|150px|Michael Faraday.]]
  
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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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The concept of electric fields was introduced by [[Michael Faraday]]. 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 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 (e.g. 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.
  
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=== Safety in power systems ===
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=== Electric potential ===
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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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{{Main|Electric potential}}
  
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=== Applications ===
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The electric potential difference between two points 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]]. The potential 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
  
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In [[electrical engineering]], the energy in electromagnetic fields is harnessed to perform useful work—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 current ===
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{{Main|Current (electricity)}}
  
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===Producing electrical energy===
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An [[electric current]] is a flow of [[electric charge]], and its intensity 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]]. See ''[[electrical conduction]]'' for more information.
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''See also: [[Electricity generation]]''
 
  
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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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Devices that use charge flow principles in materials are called [[electronics|electronic devices]].  
  
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====Hydropower====
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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. 
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''See main article: [[Hydropower]]''
 
  
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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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[[Ohm's Law]] is an important relationship describing the behaviour of electric currents, relating them to [[voltage]].
  
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====Nuclear 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.  If another definition is used - for example, "electron current" - it should be explicitly stated.
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''See main article: [[nuclear power]]''
 
  
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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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=== Electrical energy ===
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{{Main|Electrical energy}}
  
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====Solar power====
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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:
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''See main article: [[Solar power]]''
 
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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.
 
  
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====Wind power====
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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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''See main article: [[wind power]]''
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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]]
  
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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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=== Electric power ===
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{{Main|Electric power}}
  
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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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Electric power is the rate at which electrical energy is produced or consumed, and is measured in [[watt]]s (symbol is: W).  
  
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====Burning of fuel====
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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.
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''See main article: [[Fossil fuel power plant]]''
 
  
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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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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, i.e. [[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.
  
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== Electric current ==
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In electrical engineering, the concepts of [[apparent power]] and [[reactive power]] are also used. Apparent power is the product of RMS voltage and RMS current, and is measured in volt-amperes (VA). [[Reactive power]] is measured in volt-amperes-reactive (VAr).
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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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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]].  
 
  
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See [[electrical conduction]]
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Non-nuclear electric power is categorized as either green or brown electricity.
  
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[[Ohm's Law]] is an important relationship describing the behaviour of electric currents:
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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.
  
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:<math>V = I \cdot R \,</math>
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Electricity from coal, oil, and natural gas is known as traditional power or "brown" electricity.
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where
 
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<math>V</math> is the applied voltage, measured in [[volt]]s
 
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<math>I</math> is the current, measured in [[ampere]]s
 
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<math>R</math> is the resistance, measured in [[ohm]]s
 
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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.
 
  
 
== SI electricity units ==
 
== SI electricity units ==
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== See also ==
 
== See also ==
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* '''Main''': [[electromagnetism|electromagnetic]], [[electrical phenomenon|phenomenon]] ([[electric charge]]), [[electric power]] (for energy transfer using electricity), [[electric shock]], [[electric chair]] (execution)
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* [[Electromagnetism]]
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* '''Things''': [[Battery (electricity)|Battery]], [[Lightning]], [[Conductor (material)|Conductor]], [[Insulator|Insulator]], [[Leyden jar]]
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* [[Electrical engineering]]
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* '''Engineering''': [[Green electricity]], [[Electrical wiring]]
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* [[Electrical phenomena]]  
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* '''Safety''': [[High-voltage hazards]]
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* [[Electrostatics]]
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===Devices===
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* [[Battery (electricity)|Battery]]  
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* [[Electrical conductor|Conductor]]  
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* [[Insulator]]
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* [[Light fixture]]
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===Engineering===
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* [[Green electricity]]  
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* [[Electrical wiring]]
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* [[MicroCHP]]
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===Safety===
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* [[Electric shock|Electric shock and injuries]]
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* [[High voltage|High-voltage hazards]]
  
 
=== Electrical phenomena in nature ===
 
=== Electrical phenomena in nature ===
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* [[Lightning]]
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* [[Matter]]: &mdash; since [[atom]]s and [[molecule]]s are held together by electric forces.
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* [[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.
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* [[Lightning]]: electrical discharges in the atmosphere.
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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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* [[Matter]] &mdash; since [[atom]]s and [[molecule]]s are held together by electric forces.
 
 
* The [[Earth's magnetic field]] &mdash; created by electric currents circulating in the planet's core.
 
* The [[Earth's magnetic field]] &mdash; 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, which can be very damaging to sensitive electrical equipment such as [[computer]]s. However, such damage can be prevented by using a [[surge protector]].
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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]] &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.
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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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== Footnotes ==
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<references/>
  
 
== External links ==  
 
== External links ==  
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* [http://amasci.com/miscon/whatis.html  What is electricity?]
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* [http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=electricity Merriam-Webster: Electricity]
 
* [http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=electricity Merriam-Webster: Electricity]
 
* [http://www.bibliomania.com/2/9/72/119/21387/1.html Tyndall: Faraday as Discovery: Identity of Electricities]
 
* [http://www.bibliomania.com/2/9/72/119/21387/1.html Tyndall: Faraday as Discovery: Identity of Electricities]
 
* [http://www.eia.doe.gov/fuelelectric.html US Energy Department Statistics]
 
* [http://www.eia.doe.gov/fuelelectric.html US Energy Department Statistics]
 +
*[http://digital.library.unt.edu/govdocs/crs/search.tkl?q=electricity&search_crit=title&search=Search&date1=Anytime&date2=Anytime&type=form Read Congressional Research Service (CRS) Reports regarding Electricity]
 
* [http://www.mouthshut.com/readreview/38842-1.html How to save on your electricity bills]
 
* [http://www.mouthshut.com/readreview/38842-1.html How to save on your electricity bills]
 
* [http://users.pandora.be/worldstandards/electricity.htm Electricity around the world]
 
* [http://users.pandora.be/worldstandards/electricity.htm Electricity around the world]
 
* [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)  
 
* [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)  
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* [http://www.telesensoryview.com/steverosecom/Articles/UnderstandingBasicElectri.html Understanding Electricity and some Electronics in 10 minutes](Steve Rose, Maui)
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* [http://amasci.com/miscon/eleca.html Electricity Misconceptions]
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* [http://www.micro.magnet.fsu.edu/electromag/java/diode/index.html  Electricity and Magnetism]
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* [http://www.electrical-installation.merlingerin.com  Electricity and electrical installation guide]
  
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[[Category:Electricity|*]]
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[[Category:Physical sciences]]
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[[Category:Physical_sciences]]
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[[Category:Physics]]
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Revision as of 02:41, 23 November 2006

Lightning strikes during a night-time thunderstorm. As powerful electric currents flow through the Earth's atmosphere, energy is radiated as light.
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 many well-known physical phenomena such as lightning, electric fields, and electric currents, and is put to use in industrial applications such as electronics and electric power.

Concepts in electricity

In casual usage, the term electricity is applied to several related concepts that are better identified by more precise terms:

  • Electric potential (often referred to as voltage) - the potential energy per unit charge associated with a static electric field.
  • Electric current - a movement or flow of electrically charged particles.
  • Electric field - an effect produced by an electric charge that exerts a force on charged objects in its vicinity.
  • 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 charge - a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.

A spark of static electricity can measure up to three thousand (3,000) volts.

History of discovery

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, which resmbles a Galvanic cell.

Franklin kite plaque at Saint Stephen's Church, Philadelphia.

Though Benjamin Franklin's famous "invention" of electricity by flying a kite in a thunderstorm turned out to be more fiction than fact, his theories on the relationship between lightning and static electricity sparked the interest of later scientists whose work provided the basis for modern electrical technology. Most notably these include Luigi Galvani (1737–1798), Alessandro Volta (1745-1827), Michael Faraday (1791–1867), André-Marie Ampère (1775–1836), and Georg Simon Ohm (1789-1854). The late 19th and early 20th century produced such giants of electrical engineering as Nikola Tesla, Samuel Morse, Antonio Meucci, Thomas Edison, George Westinghouse, Werner von Siemens, Charles Steinmetz, and Alexander Graham Bell.

File:PbsTesla.jpg
Nikola Tesla.

Concepts in detail

Electric charge

Main article: Electric charge

Electric charge is a property of certain subatomic particles (e.g., 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: 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.

Electric field

Main article: Electric field
Michael Faraday.

The concept of electric fields was introduced by Michael Faraday. 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 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 (e.g. 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

The electric potential difference between two points 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. The potential 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 its intensity 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. See electrical conduction for more information.

Devices that use charge flow principles in materials are called electronic devices.

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 behaviour 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. If another definition is used - for example, "electron current" - it should be explicitly stated.

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

Main article: Electric power

Electric power is the rate at which electrical energy is produced or consumed, and is measured in watts (symbol is: 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, i.e. 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.

In electrical engineering, the concepts of apparent power and reactive power are also used. Apparent power is the product of RMS voltage and RMS current, and is measured in volt-amperes (VA). Reactive power is measured in volt-amperes-reactive (VAr).

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.

SI electricity units

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

Devices

Engineering

  • Green electricity
  • Electrical wiring
  • MicroCHP

Safety

Electrical phenomena in nature

  • Matter: — since atoms and molecules are held together by electric forces.
  • 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 (e.g., sharks) 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.
      • Neurons in the nervous system transmit information by electrical impulses known as action potentials.

Footnotes


External links

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