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Re: Isotropic Capacity

Subject:  Re: Isotropic Capacity
  Date:   Mon, 26 May 1997 03:08:26 +0000
  From:   "John H. Couture" <couturejh-at-worldnet.att-dot-net>
    To:   Tesla List <tesla-at-pupman-dot-com>


At 04:04 AM 5/23/97 +0000, you wrote:
>Subject:  Re: Isotropic Capacity
>  Date:  Thu, 22 May 1997 14:21:48 -0500
>  From:  David Huffman <huffman-at-FNAL.GOV>
>    To:  Tesla List <tesla-at-pupman-dot-com>
>
>
>Theory and Practice. Isotropic capacitance make perfect sense to me.
>If the object is moved infinitely far away from everything else and
>is charged, it will have its minimum 'isotropic' capacitance.
>Isotropic (adj) describes the property, capacitance (noun) that stems
>from isolating the object.
>Actually a sphere is the only object that can be isotropic by
>definition, equal properties in all axes and isotropic is a
>theoretical thing since it can't be done in actual practice.
>In a practical sense there is value in talking about the capacitance
>an object would have if it is moved away from other objects. You just
>can't completely remove it from the universe, right?
>Does a coiler really care if his toroid is 17.8pF, ten feet away from
>any object or that it is 18.2pF 2 feet off the ground? I think he
>does care that a certain size puts him in the ball park.
>Happy parasitic coiling to you!
>Dave Huffman
>snip

--------------------------------------------------------------
>> 
>>  Richard and All -
>> 
>>  Schoessow's TCBA article on isotropic capacity has unfortunately
>> mislead
>> many people. The reason is that he misinterpreted the Webster
>definition
>> for
>> "isotropic" that he quoted. Isotropic and capacitance are two words
>
>> with
>> very different meanings and do not make sense when used together.

--------------------------------------  Big snip
 
>>  John Couture
>>
-----------------------------------------------------------------

  Dave -

  An isolated sphere in space has an isotropic dielectric (space)
extending
from it in all directions to infinity. The capacitance of this sphere is
a
fixed quantity -

        pf = 1.4 D      

  where D is the diameter in inches. The sphere would have this
capacitance
regardless of where it is in the universe.

The capacitance cannot be isotropic because it is a fixed value and does
not
extend to infinity. Note that the capacitance is the same whether the
sphere
is charged or uncharged. The charging is only an indication of the
number of
coulombs on the sphere. For example, the capacitance 

        farads = Q/V 

 indicates that capacitance can be expressed as   'coulombs per volt'.

  The energy to get those coulombs on the sphere is -

        joules = .5 CV^2

  A coiler would be interested in the exact capacitance value of the
toroid
when on the top of the secondary coil because with the secondary coil
inductance it determines the operating frequency of the TC. 

The capacitance of the sphere is higher when isolated in space than when
on
the TC secondary coil. Do any coilers know why?

  John Couture