Minimum in Cmed was Re: LC and misc.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Bob (R.A.) Jones" <a1accounting@xxxxxxxxxxxxx>

Hi,

> Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>
>>
> Cmed hits a minimum for an aspect ratio of about or a bit less than 1
> if coil diameter is held constant. It climbs fairly linearly for
> 2 < h/d < 5 and then climbs substantially faster and also climbs as
> h/d drops below 1.

 Why is there a minimum in Cmed?
 This is my "hand waving" type of answer.

Approximately (?) Cmed is the isotropic capacitance  of the top half of an
isolated, bottom end grounded coil.
The isotropic C of the top half of the coil consists of two components.
The C to space and the C to the grounded half of the coil, which I will call
the Cint.
For low (<1)  h/d ratios Cint dominates because the top of the coil is close
the grounded half.
As the length increases Cint decreases as the distance between the top and
bottom of the coil increases.
While C to space increases because the top of the coil is longer.
Above h/d of 1 C to space dominated Cint, hence Cmed increases with length.

Robert (R. A.) Jones
A1 Accounting, Inc., Fl
407 649 6400