Editing Electromagnet (section)

===Core losses===
In [[alternating current]] (AC) electromagnets, used in [[transformer]]s, [[inductor]]s, and [[AC motor]]s and [[Electric generator|generators]], the magnetic field is constantly changing. This causes energy losses in their magnetic cores, which is dissipated as heat in the core. The losses stem from two processes: eddy currents and hysteresis losses.

''[[Eddy current]]s'': From [[Faraday's law of induction]], a changing magnetic field induces circulating electric currents (eddy currents) inside nearby conductors. The energy in these currents is dissipated as heat in the [[electrical resistance]] of the conductor, so they are a cause of energy loss. Since the magnet's iron core is conductive, and most of the magnetic field is concentrated there, eddy currents in the core are the major problem. Eddy currents are closed loops of current that flow in planes perpendicular to the magnetic field. The energy dissipated is proportional to the area enclosed by the loop. To prevent them, the cores of AC electromagnets are made of stacks of thin steel sheets, or [[lamination]]s, oriented parallel to the magnetic field, with an insulating coating on the surface. The insulation layers prevent eddy current from flowing between the sheets. Any remaining eddy currents must flow within the cross-section of each individual lamination, which reduces losses greatly. Another alternative is to use a [[ferrite core]], which is a nonconductor.

''[[Hysteresis loss]]es'': Reversing the direction of magnetization of the [[magnetic domain]]s in the core material each cycle causes energy loss, because of the [[coercivity]] of the material. These are called hysteresis losses. The energy lost per cycle is proportional to the area of the [[hysteresis loop]] in the ''<math>BH</math>'' graph. To minimize this loss, magnetic cores used in transformers and other AC electromagnets are made of "soft" low coercivity materials, such as [[silicon steel]] or [[soft ferrite]]. The energy loss per cycle of the alternating current is constant for each of these processes, so the power loss increases linearly with [[frequency]].