From: James Meyer
Subject: Re: Resistance of a Sphere Revisited
X-Newsreader: Forte Agent 1.92/32.572
Date: Sun, 01 Dec 2002 01:06:42 GMT
NNTP-Posting-Date: Sat, 30 Nov 2002 20:06:42 EST
On Sat, 30 Nov 2002 23:10:07 GMT, "Ed Price" wroth:
>Unless your large contact is appreciably crushing the sphere, you would have
>to assume a very small point-contact to any sphere. Imagine the contact to
>be an infinitely large, perfectly flat plane. An undistorted sphere can
>touch the plane at only one, infinitely small point.
>For the purpose of the original poster's question, lets assume the first
>sphere has a diameter of one meter, and is compared to a sphere of two
>meters diameter. Let's assume the probes each have a tiny contact area (if
>you must, make it 0.0005 square cm) in relation to the surface of either a
>one- or two-meter diameter sphere.
>Now, let's get to the geometry of the problem.
Let's instead suppose that the spheres are composed of relatively high
resistivity material. Then let's suppose contact patches of significantly lower
resistivity material plated on the poles. Connections are made to the plated
If the two spheres are proportionally contacted, then I expect the
restance will be the same for any sized sphere.
Resistivity of thin sheets like screened resistors on hybrid circuits is
usually specified in "ohms per square" "Per square what?", you may ask.
Actually, it doesn't matter. Per square cm, square inch, square meter, or
square parsec, the resistance will be the same.