Editing Electromagnetic induction (section)

==History==
[[Image:Induction experiment.png|thumb|upright=1.2|Faraday's experiment showing induction between coils of wire: The liquid battery ''(right)'' provides a current that flows through the small coil ''(A)'', creating a magnetic field. When the coils are stationary, no current is induced. But when the small coil is moved in or out of the large coil ''(B)'', the magnetic flux through the large coil changes, inducing a current which is detected by the galvanometer ''(G)''.<ref>
{{cite book|last=Poyser|first=A. W.|url=https://archive.org/details/bub_gb_JzBAAAAAYAAJ|title=Magnetism and Electricity: A Manual for Students in Advanced Classes|publisher=[[Longmans|Longmans, Green, & Co.]]|year=1892|location=London and New York|page=[https://archive.org/details/bub_gb_JzBAAAAAYAAJ/page/n298 285]}}</ref>|alt=]]
[[File:Faraday emf experiment.svg|thumb|upright=1.2|A diagram of Faraday's iron ring apparatus. Change in the magnetic flux of the left coil induces a current in the right coil.<ref name="Giancoli">{{cite book|last=Giancoli|first=Douglas C.|url=https://archive.org/details/physicsprinciple00gian|title=Physics: Principles with Applications|year=1998|edition=5th|pages=[https://archive.org/details/physicsprinciple00gian/page/623 623–624]|url-access=registration}}</ref>|alt=]]Electromagnetic induction was discovered by [[Michael Faraday]], published in 1831.<ref>{{cite book|last=Ulaby|first=Fawwaz|title=Fundamentals of applied electromagnetics|edition=5th|year=2007|url=https://www.amazon.com/exec/obidos/tg/detail/-/0132413264/ref=ord_cart_shr?%5Fencoding=UTF8&m=ATVPDKIKX0DER&v=glance|publisher=Pearson: Prentice Hall|isbn=978-0-13-241326-8|page=255}}</ref><ref>{{cite web|url=http://www.nas.edu/history/members/henry.html|title=Joseph Henry|access-date=2006-11-30|work=Distinguished Members Gallery, National Academy of Sciences|url-status=dead|archive-url=https://web.archive.org/web/20131213121232/http://www.nas.edu/history/members/henry.html|archive-date=2013-12-13}}</ref> It was discovered independently by [[Joseph Henry]] in 1832.<ref>{{cite web|last=Errede|first=Steven|author-link=Steven Errede|year=2007|title=A Brief History of The Development of Classical Electrodynamics
|url=http://web.hep.uiuc.edu/home/serrede/P435/Lecture_Notes/A_Brief_History_of_Electromagnetism.pdf}}</ref><ref>{{cite encyclopedia|encyclopedia=Smithsonian Institution Archives|title=Electromagnetism|url=http://siarchives.si.edu/history/exhibits/henry/electromagnetism}}</ref>

In Faraday's first experimental demonstration, on August 29, 1831,<ref name="aug29">{{Cite web |last=Faraday |first=Michael |date=1831-08-29 |title=Faraday's notebooks: Electromagnetic Induction |url=https://www.rigb.org/docs/faraday_notebooks__induction_0.pdf |url-status=dead |archive-url=https://web.archive.org/web/20210830003053/https://www.rigb.org/docs/faraday_notebooks__induction_0.pdf |archive-date=2021-08-30 |access-date= |website=[[The Royal Institution of Great Britain]]}}</ref> he wrapped two wires around opposite sides of an iron ring or "[[torus]]" (an arrangement similar to a modern [[toroidal transformer]]).{{citation needed|date=August 2016}} Based on his understanding of electromagnets, he expected that, when current started to flow in one wire, a sort of wave would travel through the ring and cause some electrical effect on the opposite side. He plugged one wire into a [[galvanometer]], and watched it as he connected the other wire to a battery. He saw a transient current, which he called a "wave of electricity", when he connected the wire to the battery and another when he disconnected it.<ref>''Michael Faraday'', by L. Pearce Williams, pp. 182–183</ref> This induction was due to the change in [[magnetic flux]] that occurred when the battery was connected and disconnected.<ref name="Giancoli" /> Within two months, Faraday found several other manifestations of electromagnetic induction. For example, he saw transient currents when he quickly slid a bar magnet in and out of a coil of wires, and he generated a steady ([[direct current|DC]]) current by rotating a copper disk near the bar magnet with a sliding electrical lead ("[[Faraday's disk]]").<ref>''Michael Faraday'', by L. Pearce Williams, pp. 191–195</ref>

Faraday explained electromagnetic induction using a concept he called [[lines of force]]. However, scientists at the time widely rejected his theoretical ideas, mainly because they were not formulated mathematically.<ref name=Williams510>''Michael Faraday'', by L. Pearce Williams, p. 510</ref> An exception was [[James Clerk Maxwell]], who used Faraday's ideas as the basis of his quantitative electromagnetic theory.<ref name=Williams510/><ref>Maxwell, James Clerk (1904), ''A Treatise on Electricity and Magnetism'', Vol. II, Third Edition. Oxford University Press, pp. 178–179 and 189.</ref><ref name="IEEUK">[http://www.theiet.org/about/libarc/archives/biographies/faraday.cfm "Archives Biographies: Michael Faraday", The Institution of Engineering and Technology.]</ref> In Maxwell's model, the time varying aspect of electromagnetic induction is expressed as a differential equation, which [[Oliver Heaviside]] referred to as Faraday's law even though it is slightly different from Faraday's original formulation and does not describe motional emf. Heaviside's version (see [[#Maxwell–Faraday equation|Maxwell–Faraday equation below]]) is the form recognized today in the group of equations known as [[Maxwell's equations]].

In 1834 [[Heinrich Lenz]] formulated the law named after him to describe the "flux through the circuit". [[Lenz's law]] gives the direction of the induced emf and current resulting from electromagnetic induction.