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[[Image:Lightning3.jpg|right|thumb|250px|Lightning is one of the most dramatic effects of electricity]]
'''विद्युत''' छगो कथंया उर्जा ख। थ्व उर्जा चार्ज दुगु पार्टिकल चलयमान जुइबिले पिहांवइ।
'''Electricity''' (from the [[Greek language|Greek]] word ήλεκτρον, (elektron), meaning [[amber]], and finally from [[New Latin]] ''ēlectricus'', "amber-like") is a general term that encompasses a variety of phenomena resulting from the presence and flow of [[electric charge]]. These include many easily recognizable phenomena such as [[lightning]] and [[static electricity]], but in addition, less familiar concepts such as the [[electromagnetic field]] and [[electromagnetic induction]].
In general usage, the word 'electricity' is adequate to refer to a number of physical effects. However, in scientific usage, the term is vague, and these related, but distinct, concepts are better identified by more precise terms:
* '''[[Electric charge]]''' – a property of some [[subatomic particle]]s, which determines their [[electromagnetic interaction]]s. Electrically charged matter is influenced by, and produces, electromagnetic fields.
*'''[[Electric current]]''' – a movement or flow of electrically charged particles, typically measured in [[ampere]]s.
*'''[[Electric field]]''' – an influence produced by an electric charge on other charges in its vicinity.
*'''[[Electric potential]]''' – the capacity of an electric field to do [[Work (thermodynamics)|work]], typically measured in [[volt]]s.
* '''[[Electromagnetism]]''' – a [[fundamental interaction]] between the magnetic field and the presence and motion of an electric charge.
Electricity has been studied since antiquity, though scientific advances were not forthcoming until the seventeenth and eighteenth centuries. It would not be until the late nineteenth century, however, that [[Electrical engineering|engineers]] were able to put electricity to industrial and residential use. This period witnessed a rapid expansion in the development of electrical technology. Electricity's extraordinary versatility as a source of energy means it can be put to an almost limitless set of applications which include [[motive power|transport]], [[HVAC|heating]], [[electric lighting|lighting]], [[Telecommunication|communications]], and [[computation]]. The backbone of modern industrial society is, and for the foreseeable future can be expected to remain, the use of electrical power.<ref>
{{Citation
| first = D.A. | last = Jones
| title = Electrical engineering: the backbone of society
| journal = Proceedings of the IEE: Science, Measurement and Technology
| pages = 1–10
| volume = 138
| issue = 1}}
</ref>
{{wiktionary}}
== History ==
[[Image:Thales.jpg|thumb|right|upright|Thales, the earliest researcher into electricity]]
{{main|History of electromagnetism}}
{{seealso|Etymology of electricity}}
Long before any knowledge of electricity existed people were aware of shocks from [[electric fish]]es. [[Ancient Egypt]]ian texts dating from [[2750 BC]] referred to these fish as the "Thunderer of the [[Nile]]", and described them as the "protectors" of all other fish. They were again reported millennia later by [[ancient Greek]], [[Roman Empire|Roman]] and [[Islamic geography|Arabic naturalists]] and [[Islamic medicine|physicians]].<ref>{{citation|title=Review: Electric Fish|first=Peter|last=Moller|journal=BioScience|volume=41|issue=11|date=December 1991|pages=794-6 [794]}}</ref> Several ancient writers, such as [[Pliny the Elder]] and [[Scribonius Largus]], attested to the numbing effect of [[electric shock]]s delivered by [[Electric catfish|catfish]] and [[torpedo ray]]s, and knew that such shocks could travel along conducting objects.<ref name=Electroreception>
{{citation
| first = Theodore H. | last = Bullock
| title = Electroreception
| pages = 5–7
| publisher = Springer
| year = 2005
| isbn = 0387231927}}
</ref> Patients suffering from ailments such as [[gout]] or [[headache]] were directed to touch electric fish in the hope that the powerful jolt might cure them.<ref name=morris>
{{citation
| first = Simon C. | last = Morris
| title = Life's Solution: Inevitable Humans in a Lonely Universe
| pages = 182–185
| publisher = Cambridge University Press
| year = 2003
| isbn = 0521827043}}</ref> Possibly the earliest and nearest approach to the discovery of the identity of [[lightning]], and electricity from any other source, is to be attributed to the [[Physics in medieval Islam|Arabs]], who before the 15th century had the [[Arabic language|Arabic]] word for lightning (''raad'') applied to the [[electric ray]].<ref name="EncyclopediaAmericana">''The [[Encyclopedia Americana]]; a library of universal knowledge'' (1918), [[New York]]: Encyclopedia Americana Corp</ref>
That certain objects such as rods of [[amber]] could be rubbed with cat's fur and attract light objects like feathers was known to ancient cultures around the [[Mediterranean Sea|Mediterranean]]. [[Thales of Miletos]] made a series of observations on [[static electricity]] around 600 BC, from which he believed that friction rendered amber [[magnetic]], in contrast to minerals such as [[magnetite]], which needed no rubbing.<ref name=stewart>
{{Citation
| first = Joseph | last= Stewart
| title = Intermediate Electromagnetic Theory
| publisher = World Scientific
| year = 2001
| page = 50
| isbn = 9-8102-4471-1}}
</ref><ref>
{{Citation
| first = Brian | last = Simpson
| title = Electrical Stimulation and the Relief of Pain
| publisher = Elsevier Health Sciences
| year = 2003
| pages = 6–7
| isbn = 0-4445-1258-6}}
</ref> Thales was incorrect in believing the attraction was due to a magnetic effect, but later science would prove a link between magnetism and electricity. According to a controversial theory, the [[Parthia]]ns may have had knowledge of [[electroplating]], based on the 1936 discovery of the [[Baghdad Battery]], which resembles a [[galvanic cell]], though it is uncertain whether the artefact was electrical in nature.<ref>
{{Citation
| first = Arran | last = Frood
| title = Riddle of 'Baghdad's batteries'
| publisher = BBC
| date = [[27 February]] [[2003]]
| accessdate = 2008-02-16
| url = http://news.bbc.co.uk/1/hi/sci/tech/2804257.stm}}
</ref>
[[Image:Franklin-Benjamin-LOC.jpg|thumb|left|upright|Benjamin Franklin conducted extensive research on electricity in the 18th century]]
Electricity would remain little more than an intellectual curiosity for millennia until 1600, when the English physician [[William Gilbert]] made a careful study of electricity and magnetism, distinguishing the [[lodestone]] effect from static electricity produced by rubbing amber.<ref name=stewart/> He coined the [[New Latin]] word ''electricus'' ("of amber" or "like amber", from ''ήλεκτρον'' [''elektron''], the Greek word for "amber") to refer to the property of attracting small objects after being rubbed.<ref>
{{Citation
| first = Brian | last = Baigrie
| title = Electricity and Magnetism: A Historical Perspective
| publisher = Greenwood Press
| year = 2006
| pages = 7–8
| isbn = 0-3133-3358-0}}
</ref> This association gave rise to the English words "electric" and "electricity", which made their first appearance in print in [[Thomas Browne]]'s ''[[Pseudodoxia Epidemica]]'' of 1646.<ref>
{{Citation
| first = Gordon | last = Chalmers
| title = The Lodestone and the Understanding of Matter in Seventeenth Century England
| journal = Philosophy of Science
| year = 1937
| volume = 4
| issue = 1
| pages = 75–95}}</ref>
Further work was conducted by [[Otto von Guericke]], [[Robert Boyle]], [[Stephen Gray (scientist)|Stephen Gray]] and [[C. F. du Fay]]. In the 18th century, [[Benjamin Franklin]] conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a metal key to the bottom of a dampened kite string and flown the kite in a storm-threatened sky.<ref>
{{citation
| first = James | last = Srodes
| title = Franklin: The Essential Founding Father
| pages = 92–94
| year = 2002
| publisher = Regnery Publishing
| isbn = 0895261634}} It is uncertain if Franklin personally carried out this experiment, but it is popularly attributed to him.</ref> He observed a succession of sparks jumping from the key to the back of his hand, showing that [[lightning]] was indeed electrical in nature.<ref>{{cite book
| last = Uman
| first = Martin
| authorlink = Martin A. Uman
| title = All About Lightning
| publisher = Dover Publications
| date = 1987
| url = http://ira.usf.edu/CAM/exhibitions/1998_12_McCollum/supplemental_didactics/23.Uman1.pdf
| isbn = 048625237X}}</ref>
In 1791 [[Luigi Galvani]] published his discovery of [[bioelectricity]], demonstrating that electricity was the medium by which [[nerve cell]]s passed signals to the muscles.<ref name=kirby>
{{citation
| first = Richard S. | last = Kirby
| title = Engineering in History
| pages = 331–333
| year = 1990
| publisher = Courier Dover Publications
| isbn = 0486264122}}
</ref> [[Alessandro Volta]]'s battery, or [[voltaic pile]], of 1800, made from alternating layers of zinc and copper, provided scientists with a more reliable source of electrical energy than the [[electrostatic machine]]s previously used.<ref name=kirby/> The recognition of [[electromagnetism]], the unity of electric and magnetic phenomena, is due to [[Hans Christian Ørsted]] and
[[André-Marie Ampère]] in 1819-1820; [[Michael Faraday]] invented the [[electric motor]] in 1821, and [[Georg Ohm]] mathematically analysed the electrical circuit in 1827.<ref name=kirby/>
While it had been the early 19th century that had seen rapid progress in electrical science, the late 19th century would see the greatest progress in [[electrical engineering]]. Through such people as [[Nikola Tesla]], [[Thomas Edison]], [[George Westinghouse]], [[Ernst Werner von Siemens]], [[Alexander Graham Bell]] and [[William Thomson, 1st Baron Kelvin|Lord Kelvin]], electricity was turned from a scientific curiosity into an essential tool for modern life, becoming a driving force for the [[Second Industrial Revolution]].<ref>
{{Citation
| first = Dragana | last = Marković
| title = The Second Industrial Revolution
| url= http://www.b92.net/eng/special/tesla/life.php?nav_id=36502
| accessdate = 2007-12-09}}
</ref>{{clear}}
== Concepts ==
=== Electric charge ===
{{Main|Electric charge}}
{{seealso|electron|proton|ion}}
Electric charge is a property of certain [[subatomic particle]]s, which gives rise to and interacts with, the [[electromagnetic force]], one of the four [[fundamental force]]s of nature. Charge originates in the [[atom]], in which its most familiar carriers are the [[electron]] and [[proton]]. It is a [[conserved quantity]], that is, the net charge within an [[isolated system]] will always remain constant regardless of any changes taking place within that system.<ref>
{{Citation
| first = James | last = Trefil
| title = The Nature of Science: An A-Z Guide to the Laws and Principles Governing Our Universe
| publisher = Houghton Mifflin Books
| page = 74
| year = 2003
| isbn = 0-6183-1938-7}}
</ref> Within the system, charge may be transferred between bodies, either by direct contact, or by passing along a conducting material, such as a wire.<ref name=duffin>
{{Citation
| first = W.J. | last = Duffin
| title = Electricity and Magnetism, 3rd edition
| publisher = McGraw-Hill
| pages = 2–5
| year = 1980
| isbn = 007084111X}}
</ref> The informal term [[static electricity]] refers to the net presence (or 'imbalance') of charge on a body, usually caused when dissimilar materials are rubbed together, transferring charge from one to the other.
[[Image:Electroscope.png|thumb|right|Charge on a [[gold-leaf electroscope]] causes the leaves to visibly repel each other]]
The presence of charge gives rise to the electromagnetic force: charges exert a [[force]] on each other, an effect that was known, though not understood, in antiquity.<ref name=uniphysics>
{{Citation
| first = Francis | last = Sears, ''et al.''
| title = University Physics, Sixth Edition
| publisher = Addison Wesley
| page = 457
| year = 1982
| isbn = 0-2010-7199-1}}
</ref> A lightweight ball suspended from a string can be charged by touching it with a glass rod that has itself been charged by rubbing with a cloth. If a similar ball is charged by the same glass rod, it is found to repel the first: the charge acts to force the two balls apart. Two balls that are charged with a rubbed amber rod also repel each other. However, if one ball is charged by the glass rod, and the other by an amber rod, the two balls are found to attract each other. These phenomena were investigated in the late eighteenth century by [[Charles-Augustin de Coulomb]], who deduced that charge manifests itself in two opposing forms, leading to the well-known axiom: ''like-charged objects repel and opposite-charged objects attract''.<ref name=uniphysics/>
The force acts on the charged particles themselves, hence charge has a tendency to spread itself as evenly as possible over a conducting surface. The magnitude of the electromagnetic force, whether attractive or repulsive, is given by [[Coulomb's law]], which relates the force to the product of the charges and has an [[inverse-square]] relation to the distance between them.<ref>"The repulsive force between two small spheres charged with the same type of electricity is inversely proportional to the square of the distance between the centres of the two spheres." Charles-Augustin de Coulomb, ''Histoire de l'Academie Royal des Sciences'', Paris 1785.</ref><ref>
{{Citation
| first = W.J. | last = Duffin
| title = Electricity and Magnetism, 3rd edition
| publisher = McGraw-Hill
| page = 35
| year = 1980
| isbn = 007084111X}}
</ref> The electromagnetic force is very strong, second only in strength to the [[strong interaction]],<ref>
{{citation
| last = National Research Council
| title = Physics Through the 1990s
| pages = 215–216
| year = 1998
| publisher = National Academies Press
| isbn = 0309035767}}
</ref> but unlike that force it operates over all distances.<ref name=Umashankar>
{{citation
| first = Korada | last = Umashankar
| title = Introduction to Engineering Electromagnetic Fields
| pages = 77–79
| year = 1989
| publisher = World Scientific
| isbn = 9971509210}}
</ref> In comparison with the much weaker [[gravitational force]], the electromagnetic force pushing two electrons apart is 10<sup>42</sup> times that of the [[gravitation]]al attraction pulling them together.<ref name=hawking>
{{Citation
| first = Stephen | last = Hawking
| title = A Brief History of Time
| publisher = Bantam Press
| page = 77
| year = 1988
| isbn = 0-553-17521-1}}</ref>
The charge on electrons and protons is opposite in sign, hence an amount of charge may be expressed as being either negative or positive. By convention, the charge carried by electrons is deemed negative, and that by protons positive, a custom that originated with the work of [[Benjamin Franklin]].<ref>
{{Citation
| first = Jonathan | last = Shectman
| title = Groundbreaking Scientific Experiments, Inventions, and Discoveries of the 18th Century
| publisher = Greenwood Press
| pages = 87–91
| year = 2003
| isbn = 0-3133-2015-2}}
</ref> The amount of charge is usually given the symbol ''Q'' and expressed in [[coulomb]]s;<ref>
{{Citation
| first = Tyson | last = Sewell
| title = The Elements of Electrical Engineering
| publisher = Lockwood
| page = 18
| year = 1902}}. The ''Q'' originally stood for 'quantity of electricity', the term 'electricity' now more commonly expressed as 'charge'.</ref> each electron carries the same charge of approximately −1.6022×10<small><sup>−19</sup></small> [[coulomb]]. The proton has a charge that is equal and opposite, and thus +1.6022×10<small><sup>−19</sup></small> coulomb. Charge is possessed not just by [[matter]], but also by [[antimatter]], each [[antiparticle]] bearing an equal and opposite charge to its corresponding particle.<ref>
{{Citation
| first = Frank | last = Close
| title = The New Cosmic Onion: Quarks and the Nature of the Universe
| publisher = CRC Press
| page = 51
| year = 2007
| isbn = 1-5848-8798-2}}
</ref>
Charge can be measured by a number of means, an early instrument being the [[gold-leaf electroscope]], which although still in use for classroom demonstrations, has been superseded by the electronic [[electrometer]].<ref name=duffin/>
=== Electric current ===
{{Main|Current (electricity)}}
The movement of electric charge is known as an [[electric current]], the intensity of which is usually measured in [[ampere]]s. Current can consist of any moving charged particles; most commonly these are electrons, but any charge in motion constitutes a current.
By historical convention, a positive current is defined as having the same direction of flow as any positive charge it contains, or to flow from the most positive part of a circuit to the most negative part. Current defined in this manner is called [[conventional current]]. The motion of negatively-charged electrons around an [[electric circuit]], one of the most familiar forms of current, is thus deemed positive in the ''opposite'' direction to that of the electrons.<ref>
{{Citation
| first = Robert | last = Ward
| title = Introduction to Electrical Engineering
| publisher = Prentice-Hall
| page = 18
| year = 1960}}
</ref> However, depending on the conditions, an electric current can consist of a flow of [[charged particle]]s 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 needs to be explicitly stated.
[[Image:Lichtbogen 3000 Volt.jpg|thumb|200px|left|An [[electric arc]] provides an energetic demonstration of electric current]]
The process by which electric current passes through a material is termed [[electrical conduction]], and its nature varies with that of the charged particles and the material through which they are travelling. Examples of electric currents include metallic conduction, where electrons flow through a [[Electrical conductor|conductor]] such as metal, and [[electrolysis]], where [[ion]]s (charged [[atom]]s) flow through liquids. While the particles themselves can move quite slowly, sometimes with an average [[drift velocity]] only fractions of a millimetre per second,<ref name=duffin>
{{Citation
| first = W.J. | last = Duffin
| title = Electricity and Magnetism, 3rd edition
| publisher = McGraw-Hill
| page = 17
| year = 1980
| isbn = 007084111X}}
</ref> the [[electric field]] that drives them itself propagates at close to the [[speed of light]], enabling electrical signals to pass rapidly along wires.<ref>
{{Citation
| first = L. | last = Solymar
| title = Lectures on electromagnetic theory
| publisher = Oxford University Press
| page = 140
| year = 1984
| isbn = 0-19-856169-5}}
</ref>
Current causes several observable effects, which historically were the means of recognising its presence. That water could be decomposed by the current from a voltaic pile was discovered by [[William Nicholson (chemist)|Nicholson]] and [[Anthony Carlisle|Carlisle]] in 1800, a process now known as [[electrolysis]]. Their work was greatly expanded upon by [[Michael Faraday]] in 1833.<ref name=duffin23-24>
{{Citation
| first = W.J. | last = Duffin
| title = Electricity and Magnetism, 3rd edition
| publisher = McGraw-Hill
| pages = 23–24
| year = 1980
| isbn = 007084111X}}
</ref> Current through a [[electrical resistance|resistance]] causes localised heating, an effect [[James Prescott Joule]] studied mathematically in 1840.<ref name=duffin23-24/> One of the most important discoveries relating to current was made accidentally by [[Hans Christian Ørsted]] in 1820, when, while preparing a lecture, he witnessed the current in a wire disturbing the needle of a magnetic compass.<ref name=berkson>
{{Citation
| first = William | last = Berkson
| title = Fields of Force: The Development of a World View from Faraday to Einstein
| publisher = Routledge
| page = 370
| year = 1974
| isbn = 0-7100-7626-6}} Accounts differ as to whether this was before, during, or after a lecture.</ref> He had discovered [[electromagnetism]], a fundamental interaction between electricity and magnetics.
In engineering or household applications, current is often described as being either [[direct current]] (DC) or [[alternating current]] (AC). These terms refer to how the current varies in time. Direct current, as produced by example from a [[Battery (electricity)|battery]] and required by most [[Electronics|electronic]] devices, is a unidirectional flow from the positive part of a circuit to the negative.<ref name=bird>
{{citation
| first = John | last = Bird
| title = Electrical and Electronic Principles and Technology, 3rd edition
| page = 11
| publisher = Newnes
| year = 2007
| isbn = 0-978-8556-6}}
</ref> If, as is most common, this flow is carried by electrons, they will be travelling in the opposite direction. Alternating current is any current that reverses direction repeatedly; almost always this takes the form of a [[sinusoidal wave]].<ref name=bird2>
{{citation
| first = John | last = Bird
| title = Electrical and Electronic Principles and Technology, 3rd edition
| pages = 206–207
| publisher = Newnes
| year = 2007
| isbn = 0-978-8556-6}}
</ref> Alternating current thus pulses back and forth within a conductor without the charge moving any net distance over time. The time-averaged value of an alternating current is zero, but it delivers energy in first one direction, and then the reverse. Alternating current is affected by electrical properties that are not observed under [[steady state]] direct current, such as [[inductance]] and [[capacitance]].<ref name=bird3>
{{citation
| first = John | last = Bird
| title = Electrical and Electronic Principles and Technology, 3rd edition
| pages = 223–225
| publisher = Newnes
| year = 2007
| isbn = 0-978-8556-6}}
</ref> These properties however can become important when circuitry is subjected to [[transient response|transients]], such as when first energised.
=== Electric field ===
{{Main|Electric field}}
{{seealso|Electrostatics}}
The concept of the electric [[Field (physics)|field]] was introduced by [[Michael Faraday]]. An electric field is created by a charged body in the space that surrounds it, and results in a force exerted on any other charges placed within the field. The electric field acts between two charges in a similar manner to the way that the gravitational field acts between two [[mass]]es, and like it, extends towards infinity and shows an inverse square relationship with distance.<ref name=Umashankar/> However, there is an important difference. Gravity always acts in attraction, drawing two masses together, while the electric field can result in either attraction or repulsion. Since large bodies such as planets generally carry no net charge, the electric field at a distance is usually zero. Thus gravity is the dominant force at distance in the universe, despite being much weaker.<ref name=hawking/>
[[Image:Field lines.svg|thumb|right|240px|Field lines emanating from a positive charge above a plane conductor]]
An electric field generally varies in space,<ref>Almost all electric fields vary in space. An exception is the electric field surrounding a planar conductor of infinite extent, the field of which is uniform.</ref> and its strength at any one point is defined as the force (per unit charge) that would be felt by a stationary, negligible charge if placed at that point.<ref name=uniphysics_469>
{{Citation
| first = Francis | last = Sears, ''et al.''
| title = University Physics, Sixth Edition
| publisher = Addison Wesley
| pages = 469–470
| year = 1982
| isbn = 0-2010-7199-1}}
</ref> The conceptual charge, termed a '[[test charge]]', must be vanishingly small to prevent its own electric field disturbing the main field and must also be stationary to prevent the effect of [[magnetic field]]s. As the electric field is defined in terms of [[force]], and force is a [[vector]], so it follows that an electric field is also a vector, having both [[Magnitude (mathematics)|magnitude]] and [[Direction (geometry, geography)|direction]]. Specifically, it is a [[vector field]].<ref name=uniphysics_469/>
The study of electric fields created by stationary charges is called [[electrostatics]]. The field may be visualised by a set of imaginary lines whose direction at any point is the same as that of the field. This concept was introduced by Faraday,<ref name="elec_princ_p73">
{{citation
| last = Morely & Hughes
| title = Principles of Electricity, Fifth edition
| page = 73}}</ref> whose term '[[Line of force|lines of force]]' still sometimes sees use. The field lines are the paths that a point positive charge would seek to make as it was forced to move within the field; they are however an imaginary concept with no physical existence, and the field permeates all the intervening space between the lines.<ref name="elec_princ_p73"/> Field lines emanating from stationary charges have several key properties: first, that they originate at positive charges and terminate at negative charges; second, that they must enter any good conductor at right angles, and third, that they may never cross nor close in on themselves.<ref>
{{Citation
| first = Francis | last = Sears, ''et al.''
| title = University Physics, Sixth Edition
| publisher = Addison Wesley
| page = 479
| year = 1982
| isbn = 0-2010-7199-1}}
</ref>
The principles of electrostatics are important when designing items of [[high voltage|high-voltage]] equipment. There is a finite limit to the electric field strength that may withstood by any medium. Beyond this point, [[electrical breakdown]] occurs and an [[electric arc]] causes flashover between the charged parts. Air, for example, tends to arc at electric field strengths which exceed 30 kV per centimetre across small gaps. Over larger gaps, its breakdown strength is weaker, perhaps 1 kV per centimetre.<ref name=hv_eng>
{{Citation
| first = M.S.| last = Naidu
| first2 = V.| last2 = Kamataru
| title = High Voltage Engineering
| publisher = Tata McGraw-Hill
| page = 2
| year = 1982
| isbn = 0-07-451786-4}}
</ref> The most visible natural occurrence of this is [[lightning]], caused when charge becomes separated in the clouds by rising columns of air, and raises the electric field in the air to greater than it can withstand. The voltage of a large lightning cloud may be as high as 100 MV and have discharge energies as great as 250 kWh.<ref>
{{Citation
| first = M.S.| last = Naidu
| first2 = V.| last2 = Kamataru
| title = High Voltage Engineering
| publisher = Tata McGraw-Hill
| pages = 201–202
| year = 1982
| isbn = 0-07-451786-4}}
</ref>
The field strength is greatly affected by nearby conducting objects, and it is particularly intense when it is forced to curve around sharply pointed objects. This principle is exploited in the [[lightning conductor]], the sharp spike of which acts to encourage the lightning stroke to develop there, rather than to the building it serves to protect.<ref>
{{Citation
| first = Teresa | last = Rickards
| title = Thesaurus of Physics
| publisher = HarperCollins
| page = 167
| year = 1985
| isbn = 0-0601-5214-1}}
</ref>
An electric field is zero inside a conductor. This is because the net charge on a conductor only exists on the surface. External electrostatic fields are always perpendicular to the conductors surface. Otherwise this would produce a force on the charge carriers inside the conductor and so the field would not be static as we assume.
=== Electric potential ===
{{Main|Electric potential}}
{{seealso|Voltage}}
[[Image:Panasonic-oxyride.jpg|thumb|upright|A pair of [[AA battery|AA cells]]. The + sign indicates the polarity of the potential differences between the battery terminals.]]
The concept of electric potential is closely linked to that of the electric field. A small charge placed within an electric field experiences a force, and to have brought that charge to that point against the force requires [[Mechanical work|work]]. The electric potential at any point is defined as the energy required to bring a unit test charge from an [[infinity|infinite distance]] slowly to that point. It is usually measured in [[volt]]s, and one volt is the potential for which one [[joule]] of work must be expended to bring a charge of one [[coulomb]] from infinity.<ref name=uniphysics_494>
{{Citation
| first = Francis | last = Sears, ''et al.''
| title = University Physics, Sixth Edition
| publisher = Addison Wesley
| pages = 494–498
| year = 1982
| isbn = 0-2010-7199-1}}
</ref> This definition of potential, while formal, has little practical application, and a more useful concept is that of electric [[potential difference]], and is the energy required to move a unit charge between two specified points. An electric field has the special property that it is [[Conservative force|''conservative'']], which means that the path taken by the test charge is irrelevant: all paths between two specified points expend the same energy, and thus a unique value for potential difference may be stated.<ref name=uniphysics_494/> The volt is so strongly identified as the unit of choice for measurement and description of electric potential difference that the term [[voltage]] sees greater everyday usage.
For practical purposes, it is useful to define a common reference point to which potentials may be expressed and compared. While this could be at infinity, a much more useful reference is the [[Earth]] itself, which is assumed to be at the same potential everywhere. This reference point naturally takes the name [[Ground (electricity)|earth]] or [[Ground (electricity)|ground]]. Earth is assumed to be an infinite source of equal amounts of positive and negative charge, and is therefore electrically uncharged – and unchargeable.<ref>
{{Citation
| first = Raymond A. | last = Serway
| title = Serway's College Physics
| publisher = Thomson Brooks
| page = 500
| year = 2006
| isbn = 0-5349-9724-4}}
</ref>
Electric potential is a [[scalar quantity]], that is, it has only magnitude and not direction. It may be viewed as analogous to [[temperature]]: as there is a certain 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]], or field strength, indicates the direction and magnitude of the driving force behind charge movement. Equally, electric potential may be seen as analogous to [[height]]: just as a released object will fall through a difference in heights caused by a gravitational field, so a charge will 'fall' across the voltage caused by an electric field.<ref>
{{Citation
| first = Sue | last = Saeli
| title = Using Gravitational Analogies To Introduce Elementary Electrical Field Theory Concepts
| url = http://physicsed.buffalostate.edu/pubs/PHY690/Saeli2004GEModels/older/ElectricAnalogies1Nov.doc
| accessdate = 2007-12-09}}
</ref>
The electric field was formally defined as the force exerted per unit charge, but the concept of potential allows for a more useful and equivalent definition: the electric field is the local gradient of the electric potential. Usually expressed in volts per metre, the vector direction of the field is the line of greatest gradient of potential.<ref name=duffin>
{{Citation
| first = W.J. | last = Duffin
| title = Electricity and Magnetism, 3rd edition
| publisher = McGraw-Hill
| page = 60
| year = 1980
| isbn = 007084111X}}
</ref>
=== Electromagnetism ===
{{main|Electromagnetism}}
[[Image:Electromagnetism.svg|thumb|left|140px|Magnetic field circles around a current]]
Ørsted's discovery in 1821 that a [[magnetic field]] existed around all sides of a wire carrying an electric current indicated that there was a direct relationship between electricity and magnetism. Moreover, the interaction seemed different from gravitational and electrostatic forces, the two forces of nature then known. The force on the compass needle did not direct it to or away from the current-carrying wire, but acted at right angles to it.<ref name=berkson/> Ørsted's slightly obscure words were that "the electric conflict acts in a revolving manner." The force also depended on the direction of the current, for if the flow was reversed, then the force did too.<ref>
{{Citation
| first = Silvanus P. | last = Thompson
| title = Michael Faraday: His Life and Work
| publisher = Elibron Classics
| page = 79
| year = 2004
| isbn = 142127387X}}
</ref>
Ørsted did not fully understand his discovery, but he observed the effect was reciprocal: a current exerts a force on a magnet, and a magnetic field exerts a force on a current. The phenomenon was further investigated by [[André-Marie Ampère|Ampère]], who discovered that two parallel current-carrying wires exerted a force upon each other: two wires conducting currents in the same direction are attracted to each other, while wires containing currents in opposite directions are forced apart.<ref name="elec_princ_92-93">
{{citation
| last = Morely & Hughes
| title=Principles of Electricity, Fifth edition
| pages=92–93}}</ref> The interaction is mediated by the magnetic field each current produces and forms the basis for the international [[Ampere#Definition|definition of the ampere]].<ref name="elec_princ_92-93"/>
[[Image:Electric motor cycle 3.png|thumb|The electric motor exploits an important effect of electromagnetism: a current through a magnetic field experiences a force at right angles to both the field and current]]
This relationship between magnetic fields and currents is extremely important, for it led to Michael Faraday's invention of the [[electric motor]] in 1821. Faraday's [[homopolar motor]] consisted of a [[permanent magnet]] sitting in a pool of [[Mercury (element)|mercury]]. A current was allowed through a wire suspended from a pivot above the magnet and dipped into the mercury. The magnet exerted a tangential force on the wire, making it circle around the magnet for as long as the current was maintained.<ref name=iet_faraday>
{{Citation
| last = Institution of Engineering and Technology
| authorlink = Institution of Engineering and Technology
| title = Michael Faraday: Biography
| url = http://www.iee.org/TheIEE/Research/Archives/Histories&Biographies/Faraday.cfm
| accessdate = 2007-12-09}}
</ref>
Experimentation by Faraday in 1831 revealed that a wire moving perpendicular to a magnetic field developed a potential difference between its ends. Further analysis of this process, known as [[electromagnetic induction]], enabled him to state the principal, now known as [[Faraday's law of induction]], that the potential difference induced in a closed circuit is proportional to the rate of change of [[magnetic flux]] through the loop. Exploitation of this discovery enabled him to invent the first [[electrical generator]] in 1831, in which he converted the mechanical energy of a rotating copper disc to electrical energy.<ref name=iet_faraday/> [[Faraday's disc]] was inefficient and of no use as a practical generator, but it showed the possibility of generating electric power using magnetism, a possibility that would be taken up by those that followed on from his work.
Faraday's and Ampère's work showed that a time-varying magnetic field acted as a source of an electric field, and a time-varying electric field was a source of a magnetic field. Thus, when either field is changing in time, then a field of the other is necessarily induced.<ref name=uniphysics_696-700>
{{Citation
| first = Francis | last = Sears, ''et al.''
| title = University Physics, Sixth Edition
| publisher = Addison Wesley
| pages = 696–700
| year = 1982
| isbn = 0-2010-7199-1}}
</ref> Such a phenomenon has the properties of a [[wave]], and is naturally referred to as an [[electromagnetic wave]]. Electromagnetic waves were analysed theoretically by [[James Clerk Maxwell]] in 1864. Maxwell discovered a set of equations that could unambiguously describe the interrelationship between electric field, magnetic field, electric charge, and electric current. He could moreover prove that such a wave would necessarily travel at the [[speed of light]], and thus light itself was a form of electromagnetic radiation. [[Maxwell's Laws]], which unify light, fields, and charge are one of the great milestones of theoretical physics.<ref name=uniphysics_696-700/>
==Electric circuits==
{{main|Electric circuit}}
[[Image:Ohms law voltage source.svg|thumb|200px|left|A basic [[electric circuit]]. The [[voltage source]] ''V'' on the left drives a [[Current (electricity)|current]] ''I'' around the circuit, delivering [[electrical energy]] into the [[Electrical resistance|resistance]] ''R''. From the resistor, the current returns to the source, completing the circuit.]]
An electric circuit is an interconnection of electric components, usually to perform some useful task, with a return path to enable the charge to return to its source.
The components in an electric circuit can take many forms, which can include elements such as [[resistor]]s, [[capacitor]]s, [[switch]]es, [[transformer]]s and [[electronics]]. [[Electronic circuit]]s contain [[active component]]s, usually [[semiconductor]]s, and typically exhibit [[non-linear]] behavior, requiring complex analysis. The simplest electric components are those that are termed [[passivity|passive]] and [[linear]]: while they may temporarily store energy, they contain no sources of it, and exhibit linear responses to stimuli.<ref name=ec_3>
{{citation
| first=Edminister | last=Joseph
| title=Electric Circuits
| page=3
| year=1965
| publisher=McGraw-Hill
| isbn=07084397X }}</ref>
The [[resistor]] is perhaps the simplest of passive circuit elements: as its name suggests, it [[Electrical resistance|resists]] the current through it, dissipating its energy as heat. [[Ohm's law]] is a basic law of [[circuit theory]], stating that the current passing through a resistance is directly proportional to the potential difference across it. The [[ohm]], the unit of resistance, was named in honour of Georg Ohm, and is symbolised by the Greek letter Ω. 1 Ω is the resistance that will produce a potential difference of one volt in response to a current of one amp.<ref name=ec_3/>
The [[capacitor]] is a device capable of storing charge, and thereby storing electrical energy in the resulting field. Conceptually, it consists of two conducting plates separated by a thin insulating layer; in practice, thin metal foils are coiled together, increasing the surface area per unit volume and therefore the [[capacitance]]. The unit of capacitance is the [[farad]], named after [[Michael Faraday]], and given the symbol ''F'': one farad is the capacitance that develops a potential difference of one volt when it stores a charge of one coulomb. A capacitor connected to a voltage supply initially causes a current as it accumulates charge; this current will however decay in time as the capacitor fills, eventually falling to zero. A capacitor will therefore not permit a [[steady state]] current, but instead blocks it.<ref name=ec_3/>
The [[inductor]] is a conductor, usually a coil of wire, that stores energy in a magnetic field in response to the current through it. When the current changes, the magnetic field does too, [[electromagnetic induction|inducing]] a voltage between the ends of the conductor. The induced voltage is proportional to the [[Time derivative|time rate of change]] of the current. The constant of proportionality is termed the [[inductance]]. The unit of inductance is the [[Henry (unit)|henry]], named after [[Joseph Henry]], a contemporary of Faraday. One henry is the inductance that will induce a potential difference of one volt if the current through it changes at a rate of one ampere per second.<ref name=ec_3/> The inductor's behaviour is in some regards converse to that of the capacitor: it will freely allow an unchanging current, but opposes a rapidly changing one.
== Production and uses ==
=== Generation ===
{{main|Electricity generation}}
[[Image:Parque eólico La Muela.jpg|thumb|left|Wind power is of increasing importance in many countries]]
Thales' experiments with amber rods were the first studies into the production of electrical energy. While this method, now known as the [[triboelectric effect]], is capable of lifting light objects and even generating sparks, it is extremely inefficient.<ref name=batteries>
{{citation
| first = Ronald | last = Dell
| first2 = David | last2 = Rand
| title = Understanding Batteries
| pages = 2–4
| year = 2001
| publisher = Royal Society of Chemistry
| isbn = 0854046054}}
</ref> It was not until the invention of the voltaic pile in the eighteenth century that a viable source of electricity became available. The voltaic pile, and its modern descendant, the [[Battery (electricity)|electrical battery]], store energy chemically and make it available on demand in the form of electrical energy.<ref name=batteries/> The battery is a versatile and very common power source which is ideally suited to many applications, but its energy storage is finite, and once discharged it must be disposed of or recharged. For large electrical demands electrical energy must be generated and transmitted in bulk.
Electrical energy is usually generated by electro-mechanical [[electrical generator|generators]] driven by [[steam]] produced from [[fossil fuel]] combustion, or the heat released from [[nuclear energy|nuclear reactions]]; or from other sources such as [[kinetic energy]] extracted from wind or flowing water. Such generators bear no resemblance to Faraday's homopolar disc generator of 1831, but they still rely on his electromagnetic principle that a conductor linking a changing magnetic field induces a potential difference across its ends.<ref>
{{citation
| first = Peter G. | last = McLaren
| title = Elementary Electric Power and Machines
| pages = 182–183
| year = 1984
| publisher = Ellis Horwood
| isbn = 0-85312-269-5}}
</ref> The invention in the late nineteenth century of the [[transformer]] meant that electricity could be generated at centralised [[power station]]s, benefiting from [[economies of scale]], and be [[Electric power transmission|transmitted]] across countries with increasing efficiency.<ref name=Patterson_p44-48>
{{citation
| first = Walter C. | last = Patterson
| title = Transforming Electricity: The Coming Generation of Change
| pages = 44–48
| year = 1999
| publisher = Earthscan
| isbn = 185383341X}}
</ref><ref>
{{citation
| last = Edison Electric Institute
| title = History of the Electric Power Industry
| url=http://www.eei.org/industry_issues/industry_overview_and_statistics/history
| accessdate = 2007-12-08}}
</ref> Since electrical energy cannot easily be stored in quantities large enough to meet demands on a national scale, at all times exactly as much must be produced as is required.<ref name=Patterson_p44-48/> This requires [[Electric utility|electricity utilities]] to make careful predictions of their electrical loads, and maintain constant co-ordination with their power stations. A certain amount of generation must always be held in [[Operating reserve|reserve]] to cushion an electrical grid against inevitable disturbances and losses.
Demand for electricity grows with great rapidity as a nation modernises and its economy develops. The United States showed a 12% increase in demand during each year of the first three decades of the twentieth century,<ref>
{{Citation
| last = Edison Electric Institute
| title = History of the U.S. Electric Power Industry, 1882-1991
| url=http://www.eia.doe.gov/cneaf/electricity/chg_stru_update/appa.html
| accessdate = 2007-12-08}}
</ref> a rate of growth that is now being experienced by emerging economies such as those of India or China.<ref>
{{Citation
| last = Carbon Sequestration Leadership Forum
| title = An Energy Summary of India
| url=http://www.cslforum.org/india.htm
| accessdate = 2007-12-08}}
</ref><ref>
{{Citation
| last = IndexMundi
| title = China Electricity - consumption
| url=http://www.indexmundi.com/china/electricity_consumption.html
| accessdate = 2007-12-08}}
</ref> Historically, the growth rate for electricity demand has outstripped that for other forms of energy, such as [[coal]].<ref>
{{Citation
| last= National Research Council
| authorlink = United States National Research Council
| title = Electricity in Economic Growth
| publisher = National Academies Press
| year = 1986
| page = 16
| isbn = 0309036771}}
</ref>
[[Environmental concerns with electricity generation]] have led to an increased focus on generation from [[Renewable energy|renewable sources]], in particular from [[wind power|wind-]] and [[hydropower]]. While debate can be expected to continue over the environmental impact of different means of electricity production, its final form is relatively clean.<ref>
{{Citation
| last= National Research Council
| authorlink = United States National Research Council
| title = Electricity in Economic Growth
| publisher = National Academies Press
| year = 1986
| page = 89
| isbn = 0309036771}}
</ref>
=== Uses ===
[[Image:Gluehlampe 01 KMJ.png|right|thumb|upright|The [[incandescent light bulb|light bulb]], an early application of electricity, operates by [[Joule heating]]: the passage of [[current (electricity)|current]] through [[Electrical resistance|resistance]] generating heat]]
Electricity is an extremely flexible form of energy, and has been adapted to a huge, and growing, number of uses.<ref>
{{Citation
| first = Matthew | last = Wald
| title = Growing Use of Electricity Raises Questions on Supply
| newspaper = New York Times
| url= http://query.nytimes.com/gst/fullpage.html?res=9C0CE6DD1F3AF932A15750C0A966958260
| date = [[21 March]] [[1990]]
| accessdate = 2007-12-09}}</ref> The invention of a practical [[incandescent light bulb]] in the 1870s led to [[lighting]] becoming one of the first publicly available applications of electrical power. Although electrification brought with it its own dangers, replacing the naked flames of gas lighting greatly reduced fire hazards within homes and factories.<ref>
{{Citation
| first = Peter | last = d'Alroy Jones
| title = The Consumer Society: A History of American Capitalism
| page = 211
| publisher = Penguin Books}}
</ref> Public utilities were set up in many cities targeting the burgeoning market for electrical lighting.
The [[Joule heating]] effect employed in the light bulb also sees more direct use in [[electric heating]]. While this is versatile and controllable, it can be seen as wasteful, since most electrical generation has already required the production of heat at a power station.<ref>
{{Citation
| first = Charles and Penelope | last = ReVelle
| title = The Global Environment: Securing a Sustainable Future
| publisher = Jones & Bartlett
| page = 298
| year = 1992
| isbn = 0867203218}}
</ref> A number of countries, such as Denmark, have issued legislation restricting or banning the use of electric heating in new buildings.<ref>
{{Citation
| last = Danish Ministry of Environment and Energy
| work = Denmark´s Second National Communication on Climate Change
| title = F.2 The Heat Supply Act
| url= http://glwww.mst.dk/udgiv/Publications/1997/87-7810-983-3/html/annexf.htm
| accessdate = 2007-12-09}}
</ref> Electricity is however a highly practical energy source for [[refrigeration]],<ref>
{{Citation
| first = Charles E. | last = Brown
| title = Power resources
| publisher = Springer
| year = 2002
| isbn = 3540426345}}
</ref> with [[air conditioning]] representing a growing sector for electricity demand, the effects of which electricity utilities are increasingly obliged to accommodate.<ref>
{{Citation
| first = B. | last = Hojjati
| first2 = S. | last2 = Battles
| title = The Growth in Electricity Demand in U.S. Households, 1981-2001: Implications for Carbon Emissions
| url= http://www.eia.doe.gov/emeu/efficiency/2005_USAEE.pdf
| accessdate = 2007-12-09}}
</ref>
Electricity is used within [[telecommunication]]s, and indeed the [[electrical telegraph]], demonstrated commercially in 1837 by [[William Fothergill Cooke|Cooke]] and [[Charles Wheatstone|Wheatstone]], was one of its earliest applications. With the construction of first [[First Transcontinental Telegraph|intercontinental]], and then [[Transatlantic telegraph cable|transatlantic]], telegraph systems in the 1860s, electricity had enabled communications in minutes across the globe. [[Optical fibre]] and [[Communications satellite|satellite communication]] technology have taken a share of the market for communications systems, but electricity can be expected to remain an essential part of the process.
The effects of electromagnetism are most visibly employed in the [[electric motor]], which provides a clean and efficient means of motive power. A stationary motor such as a [[winch]] is easily provided with a supply of power, but a motor that moves with its application, such as an [[electric vehicle]], is obliged to either carry along a power source such as a battery, or by collecting current from a sliding contact such as a [[Pantograph (rail)|pantograph]], placing restrictions on its range or performance.
Electronic devices make use of the [[transistor]], perhaps one of the most important inventions of the twentieth century,<ref>
{{Citation
| first = Dennis F. | last = Herrick
| title = Media Management in the Age of Giants: Business Dynamics of Journalism
| publisher = Blackwell Publishing
| year = 2003
| isbn = 0813816998}}
</ref> and a fundamental building block of all modern circuitry. A modern [[integrated circuit]] may contain several billion miniaturised transistors in a region only a few centimetres square.<ref>
{{Citation
| first = Saswato R.| last = Das
| title = The tiny, mighty transistor
| newspaper = Los Angeles Times
| date = [[2007-12-15]]
| url = http://www.latimes.com/news/opinion/la-oe-das15dec15,0,4782957.story?coll=la-opinion-rightrail}}
</ref>
== Electricity and the natural world ==
=== Physiological effects ===
{{main|Electric shock}}
A voltage applied to a human body causes an electric current through the tissues, and although the relationship is non-linear, the greater the voltage, the greater the current.<ref name=tleis>
{{Citation
| first = Nasser | last = Tleis
| title = Power System Modelling and Fault Analysis
| publisher = Elsevier
| year = 2008
| pages = 552–554
| isbn = 978-0-7506-8074-5}}
</ref> The threshold for perception varies with the supply frequency and with the path of the current, but is about 1 mA for mains-frequency electricity.<ref>
{{Citation
| first = Sverre | last = Grimnes
| title = Bioimpedance and Bioelectricity Basic
| publisher = Academic Press
| year = 2000
| pages = 301–309
| isbn = 0-1230-3260-1}}
</ref> If the current is sufficiently high, it will cause muscle contraction, [[fibrillation]] of the heart, and [[burn|tissue burns]].<ref name=tleis/> The lack of any visible sign that a conductor is electrified makes electricity a particular hazard. The pain caused by an electric shock can be intense, leading electricity at times to be employed as a method of [[torture]]. Death caused by an electric shock is referred to as [[electrocution]]. Electrocution is still the means of [[capital punishment|judicial execution]] in some jurisdictions, though its use has become rarer in recent times.<ref>
{{Citation
| first = J.H. | last = Lipschultz
| first2 = M.L.J.H. | last2 = Hilt
| title = Crime and Local Television News
| publisher = Lawrence Erlbaum Associates
| year = 2002
| page = 95
| isbn = 0805836209}}
</ref>
=== Electrical phenomena in nature ===
[[Image:Electric-eel2.jpg|thumb|right|The electric eel, ''Electrophorus electricus'']]
Electricity is by no means a purely human invention, and may be observed in several forms in nature, a prominent manifestation of which is [[lightning]]. The [[Earth's magnetic field]] is thought to arise from a [[dynamo theory|natural dynamo]] of circulating currents in the planet's core.<ref>
{{citation
|first=Thérèse |last=Encrenaz
|title=The Solar System
|page=217
|publisher=Springer
|isbn=3540002413}}
</ref> Certain crystals, such as [[quartz]], or even [[sugarcane]], generate a potential difference across their faces when subjected to external pressure.<ref name=crystallography>
{{citation
|first=José |last=Lima-de-Faria
|first2=Martin J. last2= Buerger
|title=Historical Atlas of Crystallography
|page=67
|publisher=Springer
|isbn=079230649X}}
</ref> This phenomenon is known as [[piezoelectricity]], from the [[Greek language|Greek]] ''piezein'' (πιέζειν), meaning to press, and was discovered in 1880 by [[Pierre Curie|Pierre]] and [[Jacques Curie]]. The effect is reciprocal, and when a piezoelectric material is subjected to an electric field, a small change in physical dimensions take place.<ref name=crystallography/>
Some organisms, such as [[shark]]s, are able to detect and respond to changes in electric fields, an ability known as [[electroreception]],<ref name=Biodynamics>
{{citation
| first = Vladimir & Tijana | last = Ivancevic
| title = Natural Biodynamics
| page = 602
| publisher = World Scientific
| year = 2005
| isbn = 9812565345}}
</ref> while others, termed [[electrogenic]], are able to generate voltages themselves to serve as a predatory or defensive weapon.<ref name=Electroreception/> The order [[Gymnotiformes]], of which the best known example is the [[electric eel]], detect or stun their prey via high voltages generated from modified muscle cells called [[electrocytes]].<ref name=morris/><ref name=Electroreception/> All animals transmit information along their cell membranes with voltage pulses called [[action potential]]s, whose functions include communication by the nervous system between neurons and muscles.<ref name="neural science">
{{citation
| first = E. | last = Kandel
| first2 = J. last2 = Schwartz
| first3 = T. | last3 = Jessell
| title = Principles of Neural Science
| pages = 27–28
| year = 2000
| publisher = McGraw-Hill Professional
| isbn = 0838577016}}
</ref> (Because of this principle, an electric shock can induce temporary or permanent [[paralysis]] by "overloading" the nervous system.) They are also responsible for coordinating activities in certain plants.<ref name="neural science"/>
== See also ==
* [[Ampere's rule]], connects the direction of an electric current and its associated magnetic currents.
* [[Electrical energy]], the potential energy of a system of charges
* [[Electricity market]], the sale of electrical energy
* [[Electrical phenomena]], observable events which illuminate the physical principles of electricity
* [[Electric power]], the rate at which electrical energy is transferred
* [[Electronics]], the study of the movement of charge through certain materials and devices
* [[Hydraulic analogy]], an analogy between the flow of water and electric current
== References ==
<!--See [[Wikipedia:Footnotes]] for an explanation of how to generate footnotes using the <ref(erences/)> tags-->
{{reflist|2}}
==Bibliography ==
* {{citation
| first = John | last = Bird
| title = Electrical and Electronic Principles and Technology, 3rd edition
| publisher = Newnes
| year = 2007
| isbn = 0-978-8556-6}}
* {{citation
| first = W.J. | last = Duffin
| title = Electricity and Magnetism, 3rd edition
| publisher = McGraw-Hill
| year = 1980
| isbn = 007084111X}}
* {{citation
| first=Joseph | last = Edminister
| title=Electric Circuits, 2nd Edition
| year=1965
| publisher=McGraw-Hill
| isbn=07084397X }}
* {{citation
| first=Percy | last = Hammond
| title=Electromagnetism for Engineers
| year=1981
| publisher=Pergamon
| isbn=0-08-022104-1 }}
* {{citation
| first=A.| last = Morely
| first2=E| last2 = Hughes
| title=Principles of Electricity, Fifth edition
| year=1994
| publisher=Longman
| isbn=0-582-22874-3}}
* {{citation
| first = M.S.| last = Naidu
| first2 = V.| last2 = Kamataru
| title = High Voltage Engineering
| publisher = Tata McGraw-Hill
| year = 1982
| isbn = 0-07-451786-4}}
* {{citation
| first = James| last = Nilsson
| first2 = Susan | last2 = Riedel
| title = Electric Circuits
| publisher = Prentice Hall
| year = 2007
| isbn = 978-0131989252}}
* {{citation
| first = Walter C. | last = Patterson
| title = Transforming Electricity: The Coming Generation of Change
| year = 1999
| publisher = Earthscan
| isbn = 185383341X}}
* {{citation
| first = Francis | last = Sears, ''et al.''
| title = University Physics, Sixth Edition
| publisher = Addison Wesley
| year = 1982
| isbn = 0-2010-7199-1}}
* Benjamin, P. (1898). [http://books.google.com/books?id=VLsKAAAAIAAJ A history of electricity (The intellectual rise in electricity) from antiquity to the days of Benjamin Franklin]. New York: J. Wiley & Sons.
== External links ==
{{EnergyPortal}}
* [http://www.hometips.com/hyhw/electrical/electric.html Illustrated view of how an American home's electrical system works]
* [http://users.pandora.be/worldstandards/electricity.htm Electricity around the world]
* [http://amasci.com/miscon/elect.html Electricity Misconceptions]
* [http://www.micro.magnet.fsu.edu/electromag/java/diode/index.html Electricity and Magnetism]
* [http://steverose.com/Articles/UnderstandingBasicElectri.html Understanding Electricity and Electronics in about 10 Minutes]
[[Category:Electricity|*]]
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