# Re: Speaking of resonance...

```Tesla List wrote:

> 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?

Yes. This formula is derived for an inductor with lenght >> radius.
A better approximation is (Wheeler): L=u0*N^2*area/(lenght+0.9*radius)

> ...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?

At low frequency, not, but coils are actually a kind of transmission
line,
and the high-frequency effects that come from this depend on the aspect
ratio, and on how is the coil mounted relative to the ground. For a
vertically mounted coil with the lower end grounded, the first effect
that appears is equivalent to a grounded capacitance in parallel with
the
coil, given by (units in meters) (Medhurst):