Editing Magnetic core (section)

{{Short description|Object used to guide and confine magnetic fields}}
{{for|the computer memory|Magnetic-core memory}}
A '''magnetic core''' is a piece of [[magnetism|magnetic material]] with a high [[magnetic permeability]] used to confine and guide [[magnetic field]]s in electrical, [[electromechanical]] and magnetic devices such as [[electromagnet]]s, [[transformer]]s, [[electric motor]]s, [[electric generator|generators]], [[inductor]]s, [[loudspeaker]]s, magnetic [[recording head]]s, and magnetic assemblies.  It is made of [[ferromagnetic]] metal such as iron, or [[ferrimagnetic]] compounds such as [[Ferrite (magnet)|ferrite]]s.  The high permeability, relative to the surrounding air, causes the [[magnetic field line]]s to be concentrated in the core material. The magnetic field is often created by a current-carrying coil of wire around the core.

The use of a magnetic core can increase the strength of [[magnetic field]] in an [[electromagnetic coil]] by a factor of several hundred times what it would be without the core.  However, magnetic cores have side effects which must be taken into account.  In [[alternating current]] (AC) devices they cause energy losses, called [[core losses]], due to [[hysteresis loss|hysteresis]] and [[eddy current]]s in applications such as transformers and inductors.  "Soft" magnetic materials with low [[magnetic coercivity|coercivity]] and hysteresis, such as [[silicon steel]], or [[Ferrite (magnet)|ferrite]], are usually used in cores.

[[Image:Electromagnet with gap.svg|thumb|upright=1.7|Magnetic field ''(<span style="color:green;">green</span>)'' created by a current-carrying winding ''(red)'' in a typical magnetic core transformer or inductor, with the iron core ''C'' forming a closed loop, possibly with air gaps ''G'' in it. The drawing shows a section through the core.  The purpose of the core is to provide a closed high [[permeability (electromagnetism)|permeability]] path for the magnetic field lines.<br /> 
''B'' – magnetic field in the core will be approximately constant across any cross section<br />
''B<sub>F</sub>'' – "fringing fields".  In the gaps ''G'' the magnetic field lines "bulge" out, so the field strength is less than in the core:  ''B<sub>F</sub>''&nbsp;<&nbsp;''B''<br />
''B<sub>L</sub>''  – [[leakage flux]]; magnetic field lines which don't follow complete magnetic circuit<br />
 ]]