Re: I need help.

[Bernard Cleyet <anngeorg@PACBELL.NET>]

I think I mentioned that Eisberg (Physics 1981) discusses this for buried
spheres in "Strike it rich" problem # 22-34 (electrical conductivity of the
ground for locating underground deposits)

bc

Brian Whatcott wrote:

> At 05:20 AM 2/24/02, David Bowman wrote:
> > Regarding Bernard C.'s recollection:
> >
> > > ...
> > > One of my references pointed out that the resistance between two embedded
> > > electrode spheres in the earth (rather more closely infinite embedding
> > > medium) was ~ independent of their separation > a certain minimum
> > > separation.  --IF I REMEMBER CORRECTLY.
> >
> > You do remember correctly.  As long as the two electrode spheres are
> > placed *much* farther apart from each other than each of their
> > individual radii, then the asymptotic finite resistance between them
> > is given by:  R = ([rho]/(4*[pi]))*(1/a + 1/b)  where [rho] is the
> > resistivity of the background medium and a & b are the respective
> > radii of each of the conducting electrodes spheres.
> >
> > David Bowman
> > David_Bowman@georgetowncollege.edu
>
> I am surprised that this conclusion never presented itself before to me.
> I well recall the demonstration of hammer  sounding on the lawn of some
>   campus - was it Reading U? wherein a meter square steel plate launched
> a seismic wave to reveal several proximal strata beneath using a
> microphone and pen recorder setup.
> This georheological (??)  demonstration would be just as interesting.
>
> I wonder how sensitive the determination of earth rho is to using uncovered
> copper plated steel rods of the kind often sold for grounding purposes?
>
> Brian Whatcott
>    Altus OK                      Eureka!