Editing Electromagnetic coil (section)

==Magnetic core==
Many electromagnetic coils have a [[magnetic core]], a piece of [[ferromagnetic]] material like [[iron]] in the center to increase the magnetic field.<ref name="Laplante1">{{cite book
  | last = Laplante
  | first = Phillip A. 
  | title = Comprehensive Dictionary of Electrical Engineering
  | publisher = Springer
  | year = 1998
  | page = 143
  | url = https://books.google.com/books?id=soSsLATmZnkC&dq=core&pg=PA143
  | isbn = 978-3540648352}}</ref>  The current through the coil magnetizes the iron, and the field of the magnetized material adds to the field produced by the wire. This is called a '''ferromagnetic-core''' or '''iron-core coil'''.<ref name="google7">{{cite book|title=Comprehensive Dictionary of Electrical Engineering|author=Laplante, P.A.|date=1999|publisher=Springer Berlin Heidelberg|isbn=9783540648352|url=https://books.google.com/books?id=soSsLATmZnkC&pg=PA346|page=346|access-date=2017-01-07}}</ref>  A ferromagnetic core can increase the magnetic field and [[inductance]] of a coil by hundreds or thousands of times over what it would be without the core. A '''ferrite core coil''' is a variety of coil with a core made of [[ferrite core|ferrite]], a [[ferrimagnetic]] ceramic compound.<ref name="google8">{{cite book|title=Comprehensive Dictionary of Electrical Engineering|author=Laplante, P.A.|date=1999|publisher=Springer Berlin Heidelberg|isbn=9783540648352|url=https://books.google.com/books?id=soSsLATmZnkC&pg=PA243|page=243|access-date=2017-01-07}}</ref>  Ferrite coils have lower [[core loss]]es at high frequencies.
*A coil with a core which forms a closed loop, possibly with some narrow air gaps, is called a '''closed-core''' coil.  By providing a closed path for the magnetic field lines, this geometry minimizes the [[magnetic reluctance]] and produces the strongest magnetic field. It is often used in transformers.
**A common form for closed-core coils is a '''toroidal core''' coil, in which the core has the shape of a [[torus]] or doughnut, with either a circular or rectangular cross section. This geometry has minimum [[leakage flux]] and radiates minimum [[electromagnetic interference]] (EMI).
*A coil with a core which is a straight bar or other non-loop shape is called an '''open-core''' coil.  This has lower magnetic field and inductance than a closed core, but is often used to prevent [[magnetic saturation]] of the core.
A coil without a ferromagnetic core is called an '''air-core coil'''.<ref name="google9">{{cite book|title=Comprehensive Dictionary of Electrical Engineering|author=Laplante, P.A.|date=1999|publisher=Springer Berlin Heidelberg|isbn=9783540648352|url=https://books.google.com/books?id=soSsLATmZnkC&pg=PA19|page=19|access-date=2017-01-07}}</ref> This includes coils wound on plastic or other nonmagnetic forms, as well as coils which actually have empty air space inside their windings.