Expelling an electric field.
rgrego...@yahoo.com
there a similar effect for an electric field? Note this is something
different than just an insulator not allowing a current to flow.
Bob Clark
Rene Tschaggelar
Well, a superconductor has no E field inside,
as far as I remember. No ?
Rene
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Uncle Al
Faraday cage. Depending on the EMF you wish to exclude and how much,
mesh size, skin depth, and layers of inductive and resistive loss
matter.
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http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
rgrego...@yahoo.com
> rgrego...@yahoo.com wrote:
>
> > A superconductor repels a magnetic field by the Meissner effect. Is
> > there a similar effect for an electric field? Note this is something
> > different than just an insulator not allowing a current to flow.
>
> Well, a superconductor has no E field inside,
> as far as I remember. No ?
>
> Rene
>
I hadn't heard that. Do you have a reference for this?
Bob Clark
Bob Cain
rgrego...@yahoo.com wrote:
>>Well, a superconductor has no E field inside,
>>as far as I remember. No ?
>>
>>Rene
>>
>
>
> I hadn't heard that. Do you have a reference for this?
How could it? I = (E*s)/R and R is zero.
Bob
--
"Things should be described as simply as possible, but no
simpler."
A. Einstein
Tom Roberts
This is a basic and fundamental property of any perfect conductor -- if
there were an E field inside the mobile charges would redistribute
themselves to cancel it. Look in any elementary testbook on electricity
and magnetism.
Another way to look at it is to remember that a perfect conductor is an
equipotential surface; E is the gradient of the potential, and so must
be zero.
Tom Roberts tjro...@lucent.com
Richard Saam
But there is a difference between a superconductor and a perfect conductor.
A superconductor at some dimension (less than coherence length) has a non
uniform potential surface or surfaces.
Richard Saam
Autymn D. C.
rgrego...@yahoo.com
My understanding of the Meissner effect is that if you have a hollow
sphere that is superconducting and you have a permanent magnet inside
it, then the magnetic field still exists inside the sphere: iron
fillings on the inside would be attracted to it, etc. However, no
magnetic field would be detected *outside* the superconductor from this
magnet inside. And the same would hold in reverse with the permanent
magnet outside the superconductor.
However, my reading of the effect of a charge inside a closed, hollow
perfect conductor is that the charge is redistributed to the surface of
the conductor. But then the electric field lines will still extend
outside the perfect conductor due to this charge on the surface.
What I'm looking for is for the electric field lines to be prevented
from entering or leaving the body.
Bob Clark
Tom Roberts
> Tom Roberts wrote:
>>rgrego...@yahoo.com wrote:
>>>>Well, a superconductor has no E field inside,
>
> sphere that is superconducting and you have a permanent magnet inside
> it, then the magnetic field still exists inside the sphere: iron
> fillings on the inside would be attracted to it, etc. However, no
> magnetic field would be detected *outside* the superconductor from this
> magnet inside. And the same would hold in reverse with the permanent
> magnet outside the superconductor.
Yes (ignoring some caveats about field strength at the superconductor,
etc.).
> However, my reading of the effect of a charge inside a closed, hollow
> perfect conductor is that the charge is redistributed to the surface of
> the conductor. But then the electric field lines will still extend
> outside the perfect conductor due to this charge on the surface.
Yes.
> What I'm looking for is for the electric field lines to be prevented
> from entering or leaving the body.
But they don't enter the superconductor itself -- E is zero inside the
superconductor (not necessarily its interior if it has one). But if you
want a situation in which there are also no E lines outside the sphere
then you look in vain, because unlike magnetic lines, electric lines can
begin and end (on charges, of course).
Consider a superconducting sphere with a magnet inside, and another with
a charge inside. Imagine a spherical surface outside each sphere. For
the magnet there are no magnetic lines which cross the surface. But for
the charge there are indeed electric lines which cross the surface. The
only way for there to be no E lines through that surface is for the
total charge inside the surface to be zero (and be spherically symmetric
centered on the spherical surface) -- this is known as Gauss' Law.
Tom Roberts tjro...@lucent.com