Електромоторна сила — разлика између измена
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{{Електромагнетизам}}
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'''Електромоторна сила''', скраћено '''емс''' (означава се са <math>\mathcal{E}</math> и мери у [[волт]]има),<ref>emf. (1992). ''American Heritage Dictionary of the English Language'' 3rd ed. Boston:Houghton Mifflin.</ref> величина је у [[електротехника|електротехници]] којом се изражава [[механички рад|рад]] потребан за раздвајање носилаца [[наелектрисање|наелектрисања]] у неком извору [[електрична струја|електричне струје]], при чему сила која делује на наелектрисања на крајевима извора није директна последица поља.<ref name="Stewart">{{cite book |last1=Stewart |first1=Joseph V. |title=Intermediate electromagnetic theory |date=2001 |publisher=World Scientific |page=389}}</ref> Практично говорећи - под појмом ЕМС (Електромоторна сила) подразумева се [[Електрични напон|напон]] на крајевима извора када нема струје. Чим се коло затвори и потече струја тада се на крајевима извора појављује напон који је мањи од ЕМС овог извора. Ово је последица унутрашње [[отпорности]] самог извора на којој ће се и појавити поменути пад напона. [[Ознака]] за електромоторну силу је <math>\mathcal{E}</math> ([[епсилон]]). A device that converts other forms of energy into electrical energy (a "[[transducer]]"),<ref name="Tipler803">{{cite book|last1=Tipler|first1=Paul A.|title=Physics|date=January 1976|publisher=Worth Publishers, Inc.|location=New York, NY|isbn=978-0-87901-041-6|page=803}}</ref> such as a [[Battery (electricity)|battery]] (converting [[chemical energy]]) or [[Electric generator|generator]] (converting mechanical energy),<ref name="Stewart"/> provides an emf as its output.<ref name="Tipler803"/> Sometimes an analogy to water "[[Volt#Water-flow_analogy|pressure]]" is used to describe electromotive force.<ref>{{cite journal
| journal = Transactions of the American Electrochemical Society
| title = The Relation Between Contact Potentials and Electrochemical Action
| author = Irving Langmuir
| volume = 29
| issue =
| publisher = The Society
| pages = 175
| year = 1916
| url = https://books.google.com/books?id=OW0SAAAAYAAJ&pg=PA172&dq=%22electromotive+force+is+that%22&q=%22electromotive%20force%20is%20that%22
}}</ref> (The word "force" in this case is not used to mean [[force]] of interaction between bodies, as may be measured in [[Pound (force)|pounds]] or [[newton (unit)|newtons]].)
Карактеристика сваког извора је ЕМС. Ако се при преношењу количине наелектрисања q кроз извор (од једног до другог пола) изврши рад А електромоторна сила је дефинисана формулом -{ε= A/q}-. Да би кроз електрично коло протицала струја потребно је да на крајевима проводника постоји разлика потенцијала. Сваки уређај за претварање било ког облика енергије у електричну енергију, назива се генератор, кој уједно представља и извор у струјном колу. Електромоторна сила <math>\mathcal{E}</math> је енергијска карактеристика извора и представља количник трансформисане енергије из било ког облика у електричну [dW] и количине електрицитета [dq] која протиче кроз коло електричне струје.▼
<math>\mathcal{E}</math>=dW/dq▼
In [[electromagnetic induction]], emf can be defined around a closed loop of [[electrical conductor|conductor]] as the electromagnetic [[work (physics)|work]] that would be done on an [[electric charge]] (an [[electron]] in this instance) if it travels once around the loop.<ref name=Cook>
{{cite book
| title = The Theory of the Electromagnetic Field
| author = David M. Cook
| publisher = Courier Dover
| year = 2003
| isbn = 978-0-486-42567-2
| page = 157
| url = https://books.google.com/books?id=bI-ZmZWeyhkC&pg=PA157
}}</ref> For a time-varying magnetic flux linking a loop, the electric potential scalar field is not defined due to a circulating electric vector field, but an emf nevertheless does work that can be measured as a virtual electric potential around the loop.<ref name=Lerner>
{{cite book
| title=Physics for scientists and engineers
| author=Lawrence M Lerner
| url=https://books.google.com/books?id=Nv5GAyAdijoC&pg=PA727
| publisher=Jones & Bartlett Publishers
| isbn=978-0-7637-0460-5
| pages=724–727
| year=1997}}</ref>
In the case of a two-terminal device (such as an [[electrochemical cell]]) which is modeled as a [[Thévenin's theorem|Thévenin's equivalent circuit]], the equivalent emf can be measured as the open-circuit potential difference or "voltage" between the two terminals. This potential difference can drive an [[electric current]] if an external circuit is attached to the terminals.
== Преглед ==
[[Категорија:Електрична струја]]▼
Devices that can provide emf include [[electrochemical cell]]s, [[Thermoelectric effect|thermoelectric device]]s, [[solar cells]], [[photodiode]]s, [[electrical generator]]s, [[electrical transformer|transformer]]s and even [[Van de Graaff generator]]s.<ref name=Lerner/><ref name=Tipler>
{{cite book
| title=Physics for Scientists and Engineers
|author1=Paul A. Tipler |author2=Gene Mosca | url=https://books.google.com/books?id=BMVR37-8Jh0C&pg=PA850
| page=850
| isbn=978-1-4292-0124-7
| year=2007
| edition=6
| publisher=Macmillan
}}</ref> In nature, emf is generated whenever magnetic field fluctuations occur through a surface. The shifting of the [[Earth's magnetic field]] during a [[geomagnetic storm]] induces currents in the electrical grid as the lines of the magnetic field are shifted about and cut across the conductors.
In the case of a battery, the charge separation that gives rise to a voltage difference between the terminals is accomplished by chemical reactions at the electrodes that convert chemical potential energy into electromagnetic potential energy.<ref name=Schaum>
{{cite book
|title=Schaum's outline of theory and problems of beginning physics II
|author1=Alvin M. Halpern |author2=Erich Erlbach |url=https://books.google.com/books?id=vN2chIay624C&pg=PA138
|page=138 |year=1998
|publisher=McGraw-Hill Professional
|isbn=978-0-07-025707-8
}}</ref><ref>
{{cite book
| title = Physics the easy way
| author = Robert L. Lehrman
| publisher = Barron's Educational Series
| year = 1998
| isbn = 978-0-7641-0236-3
| page = 274
| url = https://books.google.com/books?id=wMhCxOsPNE8C&pg=PA274&dq=emf++separated+charge+reaction+potential
}}</ref> A voltaic cell can be thought of as having a "charge pump" of atomic dimensions at each electrode, that is:<ref name="Singh">{{cite book|chapter-url=https://books.google.com/books?id=oS_vSI-3yuwC|title=Basic Physics|first=Kongbam Chandramani|publisher=Prentice Hall India|year=2009|isbn=978-81-203-3708-4|page=152|chapter=§3.16 EMF of a source|author=Singh}}
</ref>
== Референце ==
▲Да би кроз електрично коло протицала струја потребно је да на крајевима проводника постоји разлика потенцијала. Сваки уређај за претварање било ког облика енергије у електричну енергију, назива се генератор, кој уједно представља и извор у струјном колу. Електромоторна сила <math>\mathcal{E}</math> је енергијска карактеристика извора и представља количник трансформисане енергије из било ког облика у електричну [dW] и количине електрицитета [dq] која протиче кроз коло електричне струје.
{{reflist|}}
▲<math>\mathcal{E}</math>=dW/dq
== Литература ==
{{refbegin|30em}}
* George F. Barker, "[https://books.google.com/books?vid=0uowlltB5bCx84xQrO&id=zXAQ97d7YiIC&pg=PA649&lpg=PA650 On the measurement of electromotive force]". Proceedings of the American Philosophical Society Held at Philadelphia for Promoting Useful Knowledge, American Philosophical Society. January 19, 1883.
* Andrew Gray, "Absolute Measurements in Electricity and Magnetism", [https://books.google.com/books?vid=0pkd5YYtaGRtjR6Oes&id=WxeFSg38JLQC&pg=PA41&dq= Electromotive force]. Macmillan and co., 1884.
* Charles Albert Perkins, "Outlines of Electricity and Magnetism", [https://books.google.com/books?vid=OCLC02316583&id=jd1vvFcD-MAC&pg=PA158&vq=&dq= Measurement of Electromotive Force]. Henry Holt and co., 1896.
* John Livingston Rutgers Morgan, "The Elements of Physical Chemistry", [https://books.google.com/books?vid=OCLC10759094&id=ovjORAvJZZkC&pg=PA235&dq= Electromotive force]. J. Wiley, 1899.
* "Abhandlungen zur Thermodynamik, von H. Helmholtz. Hrsg. von Max Planck". (Tr. "Papers to thermodynamics, on H. Helmholtz. Hrsg. by Max Planck".) Leipzig, W. Engelmann, Of Ostwald classical author of the accurate sciences series. New consequence. No. 124, 1902.
* Theodore William Richards and Gustavus Edward Behr, jr., "The electromotive force of iron under varying conditions, and the effect of occluded hydrogen". Carnegie Institution of Washington publication series, 1906. {{LCCN |07003935}}
* Henry S. Carhart, "Thermo-electromotive force in electric cells, the thermo-electromotive force between a metal and a solution of one of its salts". New York, D. Van Nostrand company, 1920. {{LCCN|20020413}}
* [[Hazel Rossotti]], "Chemical applications of potentiometry". London, Princeton, N.J., Van Nostrand, 1969. {{ISBN|0-442-07048-9}} {{LCCN |69011985}}
* Nabendu S. Choudhury, 1973. [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730015362.pdf "Electromotive force measurements on cells involving beta-alumina solid electrolyte"]. NASA technical note, D-7322.
*{{cite book |title=Modern Electrochemistry: An Introduction to an Interdisciplinary Area |author1=John O'M. Bockris |author2=Amulya K. N. Reddy |chapter-url=https://books.google.com/books?id=5OGsg_v_7yoC&pg=PA647 |chapter=Electrodics |isbn=978-0-306-25002-6 |year=1973 |edition=2 |publisher=Springer}}
*{{cite journal |author=Roberts, Dana |title= How batteries work: A gravitational analog |journal= Am. J. Phys.|volume= 51 |issue= 9 |page= 829 |year=1983 |doi=10.1119/1.13128|bibcode = 1983AmJPh..51..829R }}
* G. W. Burns, et al., "Temperature-electromotive force reference functions and tables for the letter-designated thermocouple types based on the ITS-90". Gaithersburg, MD : U.S. Dept. of Commerce, National Institute of Standards and Technology, Washington, Supt. of Docs., U.S. G.P.O., 1993.
* {{cite book |author=Norio Sato |title=Electrochemistry at metal and semiconductor electrodes |page=326 ''ff'' |chapter-url=https://books.google.com/books?id=olQzaXNgM74C&pg=PA328 |isbn=978-0-444-82806-4 |year=1998 |publisher=Elsevier |edition=2nd |chapter= Semiconductor photoelectrodes}}
* {{cite journal|date=2009-03-08|title=Electromotive force and huge magnetoresistance in magnetic tunnel junctions|journal=[[Nature (journal)|Nature]]|url=http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature07879.html|accessdate=2009-03-10| doi= 10.1038/nature07879|last1=Hai|first1=Pham Nam|last2=Ohya|first2=Shinobu|last3=Tanaka|first3=Masaaki|last4=Barnes|first4=Stewart E.|last5=Maekawa|first5=Sadamichi|volume=458|pages=489–92|pmid=19270681|issue=7237|bibcode = 2009Natur.458..489H }}
{{refend}}
== Спољашње везе ==
{{Commons category|Electromotive force}}
{{Authority control}}
{{DEFAULTSORT:Електромоторна сила}}
▲[[Категорија:Електрична струја]]
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