Re: [TCML] Capacitor Conundrum

["Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>]

Sfxneon@xxxxxxx wrote:
> Hi Everyone,
>  
> Is it true that the charge of a capacitor is stored in it's  dielectric and 
> not the plates, and if so, how and where is the charge stored in  a vacuum 
> capacitor?
The charges stay at the surfaces of the conductors facing the 
dielectric. But
if the electric field is strong enough, and there is a small space 
between the
plates and the dielectric, as in the case of that dissectible Leyden 
jar, they
may leak to the surface of the dielectric.
Note that the charges are just excess of lack of electrons in some atoms.
Actually in a quite small portion of the atoms at the plate surfaces. It is
easy to verify that if you take just one electron from one in 100000 of the
atoms in a flat surface, the electric field is intense enough to ionize 
air and
produce sparks.
A "dielectric" is not just an insulator, otherwise we would not have to 
take
into account a dielectric constant different from the one of vacuum when 
dealing
with them between plates. When an electric field is applied, some 
polarization
occurs inside the dielectric, as if many capacitors in series were inserted
between the plates. The effect is an increase in the capacitance greater 
than
the one just due to the smaller distance between the plates.
A capacitor with two terminals is actually three capacitors. The one 
between the
plates and two others from the terminals to the surroundings (or to infinity
if there is nothing very close). If the plates are close, the "normal" 
capacitance
is dominant. If the plates are far apart, the "self" capacitances of the 
plates
dominate and store the charge.

Antonio Carlos M. de Queiroz



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