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Re: Isotropic Capacity

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.
The
> definitins are:
> 
>  1. Capacitance - The property of an object to store a quantity of
> electricity (coulombs).     C = Q/V.    Capacitance varies with the
> size,
> dielectric, etc.
> 
>  2. Isotropic - The property of an object that extends equally in
all
> directions from an object. For example, a charged object produces
> electric
> lines of force extending equally in all directions.
> 
> The capacitance and isotropic properties are different properties
and
> require different measurements.  R Hull measured the capacitance
but not
> the
> isotropic properties of " real terminals'. The isotropic properties
are
> lines of electric force which are not capacitance and are difficult
to
> measure.
> 
>  The sun is an example of producing isotropic light because the
light
> from
> the sun extends equally in all directions. Note that it would be
> incorrect
> to say the sun has isotropic mass. The mass does not extend in all
> directions as does the light. 
> 
> A light bulb cannot have isotropic light because of the metal base
that
> prevents an equal distribution of light in all directions. Note
that it
> would be incorrect to say that the ligh bulb has isotropic watts
because
> watts does not extend beyond the bulb.
> 
>  An isolated sphere in space that is not charged does not have
isotropic
> properties or electric lines of force. However, it does have the
> property of
> capacitance or the ability to store an electrical charge. It would
be
> incorrect to say that it has isotropic capacitance.
> 
>  An isolated sphere in space that is charged has both isotropic and
> capacitance properties. This could vagely be called an isotropic
> capacitance. The electric lines of force due to the charges would
extend
> equally in all directions.
> 
>  Tesla terminals that are charged are non-isotropic because the
electric
> lines of force are not equally extended around the terminal.
However,
> they
> do have the property of capacitance and the ability to store
electrical
> charges. Schoessow's article gives the equations for finding the
> capacitance
> of various size terminals.. Saying that these terminals have
isotropic
> capacitance would be incorrect.  
> 
>  When a metal sphere or TC Terminal is brought near the ground or
other
> object the capacitance will change. If they are charged the
electric
> lines
> of force around the sphere or terminal will not be equally divided
and
> this
> condition is non-isotropic. However, it should be noted that the
> non-isotropic property is not directly related to the capacitance.
It is
> obvious that the words "isotropic capacitance" do not make sense.
> 
>  Measuring the capacitance of a  TC terminal while it is moved
toward or
> away from ground in relatively easy. However, measuring the
> non-isotropic
> properties would be a tedious job as it would require drawings
showing
> many
> lines of electrical forces around the terminal.
> 
>  It is interesting to note that radio engineers use an isotropic
antenna
> as
> a theoretical reference for the gain of real world antennas. This
> reference
> antenna is isotropic because it is considered as radiating
> electromagnetic
> fields equally in all directions. Capacitance is not involved.
> 
>  John Couture
>