Date: Thu, 24 Feb 2011 07:38:11

Author: Cliff Bettis

Subject: Re: Tin Foil Capacitor



You'll notice in that Wiki article under the "Practical Dielectric" section
it mentions electrets. Also you can read about the frequency dependence and
the imaginary part of the dielectric constant in the article on


-----Original Message-----
From: [] On
Behalf Of Jerry DiMarco
Sent: Wednesday, February 23, 2011 4:57 PM
Subject: Re: [tap-l] Tin Foil Capacitor

These are good questions to ask, I was thinking about them last
night. Halliday and Resnick 2nd ed. states that the polarization of the
dielectric material remains only as long as the electric field is
there. So that seems to suggest that in order for the dissectible cap demo
to work, there must be something to maintain the electric field after the
plates are removed. One possibility, as JH stated, is that charge is
deposited on the dielectric surface from the plates. Are there other
possibilities? In an electrolytic capacitor there is an oxide coating on
the aluminum plate that serves as the dielectric. Where does the charge
reside in that situation?
The Wiki page on "dielectric" suggests that the dielectric constant
refers to a material's polarizability. But comparing dielectric constants
and polarizabilities of materials in the Handbook of Chem and Phys shows no
clear relationship. So there must be additional properties that determine
a material's dielectric constant. Is the ability to hold surface charge
one of those factors?


At 2/23/2011 08:43 AM, you wrote:
>What happens to the electric field inside the dielectric when the
>adjoining plate is removed? Is it pinned there? Is it weaker or stronger
>because there is no conducting surface to "terminate" the field lines?

From Thu Feb 24 08:38:32 2011