Editing Electromagnetic coil (section)

{{Short description|Electrical component}}
{{Redirect-multiple|2|Winding|Windings|the font|Wingdings|other uses|Winding (disambiguation)}}
[[File:Magnetic field of loop 3.svg|thumb|The magnetic field lines ''(<span style="color:green;">green</span>)'' of a current-carrying loop of wire pass through the center of the loop, concentrating the field there]]

An '''electromagnetic coil''' is an electrical [[Electrical conductivity|conductor]] such as a [[wire]] in the shape of a [[wiktionary:coil|coil]] ([[spiral]] or [[helix]]).<ref name="Stauffer">{{cite book
  | last = Stauffer
  | first = H. Brooke 
  | title = NFPA's Pocket Dictionary of Electrical Terms
  | publisher = Jones and Hymel Tucker
  | year = 2002
  | page = 36
  | url = https://books.google.com/books?id=9sW_knz5P0wC&pg=PA36
  | isbn = 978-0877655992}}</ref><ref name="Laplante">{{cite book
  | last = Laplante
  | first = Phillip A. 
  | title = Comprehensive Dictionary of Electrical Engineering
  | publisher = Springer
  | year = 1999
  | pages = 114–115
  | url = https://books.google.com/books?id=soSsLATmZnkC&dq=coil&pg=PA114
  | isbn = 978-3540648352}}</ref>  Electromagnetic coils are used in [[electrical engineering]], in applications where [[electric current]]s interact with [[magnetic field]]s, in devices such as [[electric motor]]s, [[Electric generator|generator]]s, [[inductor]]s, [[electromagnet]]s, [[transformer]]s, sensor coils such as in medical  [[Magnetic resonance imaging|MRI]] imaging machines.  Either an electric current is passed through the wire of the coil to generate a magnetic field, or conversely, an external ''time-varying'' magnetic field through the interior of the coil generates an [[Electromotive force|EMF]] ([[voltage]]) in the conductor.

A current through any conductor creates a circular magnetic field around the conductor due to [[Ampere's circuital law|Ampere's law]].<ref name="Arun">{{cite book
  | last = Arun
  | first = P. 
  | title = Electronics
  | publisher = Alpha Sciences International Ltd.
  | year = 2006
  | pages = 73–77
  | url = https://books.google.com/books?id=HsavX0cnxTcC&pg=PA73
  | isbn = 978-1842652176}}</ref>  The advantage of using the coil shape is that it increases the strength of the magnetic field produced by a given current.  The magnetic fields generated by the separate turns of wire all pass through the center of the coil and add ([[Superposition principle|superpose]]) to produce a strong field there.<ref name="Arun" />  The greater the [[number of turns]] of wire, the stronger the field produced. Conversely, a ''changing'' external magnetic flux induces a voltage in a conductor such as a wire, due to [[Faraday's law of induction]].<ref name="Arun" /><ref>{{cite book| url = https://books.google.com/books?id=lROa-MpIrucC&dq=Faradays+law&pg=PA129| title = Newnes 2002, p. 129| isbn = 9780080524054| last1 = Amos| first1 = S. W.| last2 = Amos| first2 = Roger| date = 4 March 2002| publisher = Elsevier}}</ref>  The induced voltage can be increased by winding the wire into a coil because the field lines intersect the circuit multiple times.<ref name="Arun" />

The direction of the magnetic field produced by a coil can be determined by the [[right hand grip rule]].  If the fingers of the right hand are wrapped around the magnetic core of a coil in the direction of [[conventional current]] through the wire, the thumb will point in the direction the [[magnetic field line]]s pass through the coil.  The end of a magnetic core from which the field lines emerge is defined to be the North pole.

There are many different types of coils used in electric and electronic equipment.

[[File:VFPt Solenoid correct2.svg|thumb|In a coil of multiple turns of wire the magnetic field of the turns adds in the center of the coil, creating a strong field.  This drawing shows a cross section through the center of the coil.  The crosses are wires in which current is moving into the page; the dots are wires in which current is emerging from the page.]]