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What is a dielectric medium?
Lots of materials are very poor conductors of electricity, because they
have almost no charges free to move around very far. Nevertheless,
every material has charges that can displace a little bit when bonds
stretch under the influence of an electric field. So in addition to the
field from the outside, there's an opposite field from all those
slightly displaced electrons etc. Such materials (non-conducting) are
At high frequencies of applied ac fields, the internal current
flowing from those locally moving charges can exceed the currents from
ordinary conduction even in materials like water, which is not a good
A dielectric medium is just one in which these dielectric effects
are more important than long-range conduction. That includes lots of
(republished on 08/02/06)
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