Editing Electromagnetic induction (section)

===Electromagnet laminations===
[[File:Hawkins Electrical Guide - Figure 292 - Eddy currents in a solid armature.jpg|thumb|upright=0.9|left]]
Eddy currents occur when a solid metallic mass is rotated in a magnetic field, because the outer portion of the metal cuts more [[magnetic lines of force]] than the inner portion; hence the induced electromotive force is not uniform; this tends to cause electric currents between the points of greatest and least potential. Eddy currents consume a considerable amount of energy and often cause a harmful rise in temperature.<ref name="Imagesand">Images and reference text are from the public domain book: ''[[Hawkins Electrical Guide]]'', Volume 1, Chapter 19: Theory of the Armature, pp. 270–273, Copyright 1917 by Theo. Audel & Co., Printed in the United States</ref>
{{clear}}
[[File:Hawkins Electrical Guide - Figure 293 - Armature core with a few laminations showing effect on eddy currents.jpg|thumb|upright=0.9|left]]
Only five laminations or plates are shown in this example, so as to show the subdivision of the eddy currents. In practical use, the number of laminations or punchings ranges from 40 to 66 per inch (16 to 26 per centimetre), and brings the eddy current loss down to about one percent. While the plates can be separated by insulation, the voltage is so low that the natural rust/oxide coating of the plates is enough to prevent current flow across the laminations.<ref name="Imagesand" />
{{clear}}
[[File:Small DC Motor pole laminations and overview.jpg|thumb|upright=0.9|left]]
This is a rotor approximately 20&nbsp;mm in diameter from a DC motor used in a {{nowrap|CD player.}} Note the laminations of the electromagnet pole pieces, used to limit parasitic inductive losses.
{{clear}}