# Re: Speaking of resonance...

```In a message dated 12/12/98 2:49:54 AM Mountain Standard Time,
tesla-at-pupman-dot-com writes:

>
>  For one, I know the general physics surrounding inductors, but tell me
>  this:  they make -- If I buy a spool of laquered copper wire and whip
>  myself up a coil, would there be any other physical properties that would
>  significantly deviate this coil from the ideal L = (Mu0*N^2*Area)/Length?
>  ...Besides the thing burning up from resistance? Will an extremely long,
>  thin coil wound with thick wire have the same properties of an equally
>  inductive very short coil of large area and high N^2/l ratio?
>
>  If this isn't true, which I'm thinking it is because I hardly ever see
>  high-current inductors for sale among hobbyists (making me think it's
>  easier just to wind one yourself).
>
First, the classical formula you wrote is valid for really long, small
diameter coils.   For Tesla coils, the best geometry is where the ratio of the
length of the coil(not the wire length) to the coil diameter is in the range
of   3:1 to 5:1.  This is not set in stone, but is the usual design.   The
inductance of such a coil is better calculated using the Wheeler equation.  L
= (r^2 x N^2)/(9r +10b)   where b = the length of the coil.
>
>  And also, I'm trying to sell these huge pulse-discharge caps, partially to
>  fund a high-voltgae club starting up down here in south florida, and
>  partially to fix my car.  I figured there'd be good demand for that kind
>  of stuff 'round the tesla coil circuit... But does anyone know the address
>  to the High Voltage list?  ...Or anyone else that might need these things?
>
What type and price for the caps?  I am sure there are some on this list who
will be interested.
Hope this helps.
Mike

```