Bob Masta wrote:
On Fri, 03 Dec 2010 11:01:33 -0500, Phil Hobbs
wrote:

snip
I'm not the worst offender, though. A lot of the explanations you hear
about physics have as much merit as the Friday afternoon stock market
guy 'explaining' what happened on Wall Street that week. The idea that
an electret mic is a variety of capacitance mic is one example...snip

OK, I'll bite: What's wrong with explaining electrets as
permanently polarized capacitance mics? Are you saying
that this is *not* the basic concept, or that it just
doesn't go deep enough to do justice?

If you have a surface with a nonzero net charge density on its surface
(so that it produces an electric field in the air), a small current will
flow due to air ions and surface water films. Therefore no object can
produce an external field forever without a power source.

Electrets are just poled piezoelectrics.

Cheers

Phil Hobbs

When you

Like the various "electricity as a flowing liquid"
analogies, sometimes a flawed analogy can nevertheless help
get a basic concept across... as long as it's clear that it
is an analogy and not an equivalence.

Best regards


Bob Masta

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
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