Re: Toward the equilibrium

[Tim Folkerts <tfolkert@FHSU.EDU>]

 At 17:28 1/3/01 -0500, Ludwik wrote:
> Suppose that at t=0 a charge of 1 microC is deposited at one
> point of a copper sphere whose diameter is one meter. I used
> to say that "the equilibrium is going to be established very
> quickly, perhaps in a couple of nanoseconds or so. Why?
> Because it can not be faster than  3.3 ns; the time light
> needs to cover the distance of 1 m in air.
>
> 1) Do charges travel to final destinations through the entire
> volume or do they travel mostly near the surface?
Neither!  The +1 uC doesn't travel through the conductor at all!  (But I'll
admit I never thought about it until you asked ....)

You need to start before t=0.  As the +1 uC is brought close to the
conductor, the electrons in the copper are already rearranging themselves.
The point on the conductor nearest the external charge will have a -1 uC
charge, while the rest will have a +1 uC surface charge.  When the external
charge finally reaches the conductor at t=0, it only needs to travel to the
-1 uC of electrons waiting at the nearest side.

No significant travel of electrons will be needed to establish equilibrium.
Other than a little "ringing", it seems that equilibrium is established AT
t=0.  Come to think of it, perhaps the "ridiculous" answer that someone
quoted and I already deleted :-(  of something like 10^-18 s actually is
correct.


Tim Folkerts
FHSU