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electret


Hmmmm.  Could be an 'electret'.  An electret (named by analogy to a
magnet) is a 'permananent electric', in the same sense a permanent
magnet is a permanent magnet.  A couple of different effects can be
storing charge on an insulator.  Charge on the surface will leak away
fairly rapidly. Charge in the 'inside' of the bulk of the dielectric[1]
will take longer to disipate.  [I would not have expected a Tesla Coil
secondary form to store charge, since the discharge is oscillatory,
but, i have been wrong before... 8)>>].

In the case of a tesla secondary, there are a couple of different sets
of dielectrics.  The one on the wire and the one of the form, per se.
Either can store charge either on the surface, or "inside".  The charge
'inside" can take a while to leak off, and is generally considered when
discussing an electret, per se.  The same effect shows up (as noted by
others) in other situations.  It can be a nuiance in low voltage work,
where a capacitor is storing a voltage to be measured as the voltage lags
(other than straight RC) applied voltage changes.  Basically, the charge
gets 'stuck' inside the dielectric (it IS an insulator.  8)>>) and takes
a while to work its way out.

Classic recipe for an electret:
	Heat some wax in a form, say like a bar.
	While molten, apply an external DC field.
	Let cool with field applied.

The filed aligns the atoms non randomly, and they get 'stuck' in a non
electrically neutral configuration.

The resultant 'electret' will have a quasi permanent electrical field.
Same trick can be done with plastics, yielding more permanence, for the
popular 'electret mike'.

[1]
An interestng experiment would be to try the test with an 'air wound' secondary.
If, in fact, charge is being stored in the form, an air wound coil should
store little charge, since it has no form...

regards
	dwp