Electret |
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A sheet of polymer is charged by placing it between parallel charged metal plates. On removal, if the opposite faces of the polymer slab retain their opposite charges, the polymer is said to be a permanently polarized electret.
An electret, as the name implies, is the electrical equivalent of a permanent magnet. An electret retains its polarization below a certain temperature and it can be discharged by placing it in an opposite electric field of sufficient strength. [To completely discharge an electret it is placed in an oscillating electric field which is slowly reduced to zero.] |
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| Note: unlike a permanent magnet, an electret is more of a curiosity than a practical device. |