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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Electromagnetic induction | 3/3 | https://en.wikipedia.org/wiki/Electromagnetic_induction | reference | science, encyclopedia | 2026-05-05T10:55:06.297489+00:00 | kb-cron |
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.
This is a rotor approximately 20 mm in diameter from a DC motor used in a CD player. Note the laminations of the electromagnet pole pieces, used to limit parasitic inductive losses.
=== Parasitic induction within conductors ===
In this illustration, a solid copper bar conductor on a rotating armature is just passing under the tip of the pole piece N of the field magnet. Note the uneven distribution of the lines of force across the copper bar. The magnetic field is more concentrated and thus stronger on the left edge of the copper bar (a,b) while the field is weaker on the right edge (c,d). Since the two edges of the bar move with the same velocity, this difference in field strength across the bar creates whorls or current eddies within the copper bar. High current power-frequency devices, such as electric motors, generators and transformers, use multiple small conductors in parallel to break up the eddy flows that can form within large solid conductors. The same principle is applied to transformers used at higher than power frequency, for example, those used in switch-mode power supplies and the intermediate frequency coupling transformers of radio receivers.
== See also ==
Alternator – Device converting mechanical into electrical energy Crosstalk – Signals in one channel affecting another Faraday paradox – Apparent paradox with Faraday's law of induction Fleming's right-hand rule – Mnemonic for the direction of induced current in a moving magnetic field Hall effect – Electromagnetic effect in physics Inductance Moving magnet and conductor problem
== References ==
=== Notes ===
=== References ===
== Further reading == Maxwell, James Clerk (1881), A treatise on electricity and magnetism, Vol. II, Chapter III, §530, p. 178. Oxford, UK: Clarendon Press. ISBN 0-486-60637-6.
== External links == Media related to Electromagnetic induction at Wikimedia Commons The Laws of Induction - The Feynman Lectures on Physics A free java simulation on motional EMF