Re: Understanding fields, capacitance and potential

to: Scott

The physics behind the equations for capacitance essentially state the
value of capacitance is dependent only on the physical geometry of the
capacitor (same true for inductors).  Copper and alum. should have the same

A single toroid in empty space will still possess isotropic capacitance due
to its surface area.  The field lines still extend to infinity and are
always relavent to something.

Stacked toroids have more capacitance than a single unit.  The usual value
is 1.5 x single value.  This does vary somewhat depending on the degree of


> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Understanding fields, capacitance and potential
> Date: Sunday, January 03, 1999 12:31 PM
> Original Poster: Scott Stephens <Scott2-at-mediaone-dot-net> 
> I'm writing this to help clarify the understanding of some coiler's who
> questions like:
> "Will two stacked torroids have more capacitance than seperated ones?"
> "Will an aluminum torroid have more capacitance than a copper one?" and
> "How can a single isolated terminal have capacitance?"
> I have wondered the same things because I often read about practical
> from vendors, for the purpose of building projects, years before studying
> the theory behind them in school.
> First understand empty space (vacuum) has the ability to be stressed by
> electric potential or voltage, in a positive or negative direction. A
> 2-dimensional metaphor is a rubber sheet, warped into a pit or peak by a
> heavy mass above or an upward force from below.
> The fundamental property that warps space electricaly is charge.
> and protons have charge. It takes more charge to electricaly warp a
> space to a given voltage, than a smaller one. The more charge in a
> area, the higher the voltage or potential, and the more energy density.
> Charge = capacitance * voltage, or Q=CV.
> Energy = 1/2 capacitance * voltage^2 (voltage^2 means voltage squared).
> Think about the amount of force it takes to warp the sheet, with
> shaped tools. The distance the sheet is warped is analagous to voltage.
> area of the tool used on the sheet determines how the force is applied
> how much energy is stored in the sheet's strain. A large area tool will
> require more effort (work or energy) to displace the sheet than a small
> Analagously, it has more capacitance.
> If two tools, or an irregularly shaped tool is used to warp the sheet,
> impression by the tools in the sheet will blur as distance from the sheet
> increases. Capacitance is charge storage capacity (like a compressed air
> bottle or spring) and surface area does not directly correlate to
> capacitance or stored charge.
> Field mapping can be used to plot the direction of the electric field and
> the amount of strain. Imagine grid lines on the rubber sheet. Poke the
> with a tool, and watch the sheet, and its grid, warp. The direction the
> lines now take plot the electric field's voltage gradient (slope). The
> seperation of the lines determine the energy storage for a given area.
> Knowing the shape of a terminal, tells you the nature of the field it
> produces, and averaging the strains over the whole surface (inegrating)
> give you capacitance.
> It doesn't matter what the tool is made of: aluminum, brass, iron. But it
> does matter what the "space" is made of. If you increase the thickness or
> stiffness of the rubber sheet in the mechanical analog, it will take more
> average force or energy to move it to the same potential as a thinner or
> looser rubber sheet.
> Since molecules are made of charged particles, they, depending on
> structure, will be more 'springy' than empty space. In fact if you take a
> material such as aluminum, electro-chemicaly treat it to increase its
> surface area, and form an insulating dielectric, it can have 1000's of
> more capacitance than empty space.
> A wonderfull tutorial about this is on the net. Do a web search for
> "Faraday-net" and electrolytic capacitors.
> Hopefully, this has been instructive, and will motivate those lurking
> God's to answer my lame queries in the future, which seldom elicit a
> responce. If I have mistated facts, or you can explain this topic more
> succinctly, please correct me and do it!