From: gherold@teachspin.com   
      
   On Wednesday, February 20, 2019 at 10:28:42 PM UTC-5, John Larkin wrote:   
   > On Tue, 19 Feb 2019 21:57:05 -0800 (PST), RichD   
   >  wrote:   
   >   
   > >On February 12, Phil Hobbs wrote:   
   > >>>>> A 1-cm radius isolated sphere has a self-capacitance of 1 cm (Gaussian   
   > >>>>> units), which is about 1.12 pF.   
   > >>   
   > >>>> Well, I have in mind your basic two plate capacitor.   
   > >>>> I don't recall self-capacitance -   
   > >>   
   > >>> Self-capacitance is the capacitance of an object with respect to   
   > >>> ground, when it is in a large grounded box.   An infinite box, ideally.   
   > >>   
   > >>   
   > >> Ground isn't necessary.  An isolated conductor with a certain amount Q   
   > >> of free charge on it will have an E field.  The voltage V is minus the   
   > >> line integral of E dot ds from the surface to infinity.  The   
   > >> self-capacitance is Q/V.   
   > >   
   > >Then infinity represents the reference point, at potential zero.   
   > >   
   > >The problem is, in this model, 'infinity' isn't a point,   
   > >but a spherical surface.   
   >   
   > A couple of light-years away is probably good enough.   
   >   
   > Need long test leads.   
   The moon will be far enough away.   
   A conducting sphere at the moon orbit would change the Earth's C   
   by less than 1%.   
   http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capsph.html   
      
   George H.   
      
   >   
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   > John Larkin         Highland Technology, Inc   
   >   
   > lunatic fringe electronics   
      
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