# Re: math woes

```Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
>
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
>
> At 10 kHz with the semiconducting nature of the body, the skin depth will be
> huge (comparable to the size of the body), so conventional formulae won't
> work.  The classical formula is for the depth in an infinite flat sheet.
> For any reasonable sized round conductor (where the "infinite flat plate"
> skin depth is a significant fraction of the radius (say >.1 r) ), there is a
> correction factor that needs to be applied.
>
> Classical formula: skin depth(meters) = sqrt(rho/(pi*f*mu))
> rho = resistivity in ohm meters
> f = frequency (Hertz)
>
> So, for your example: mu = 4 pi 1E-7, rho = 70, f = 1E4
> =sqrt(70/(4*3.14159E-7 * 1E4 * 3.14159)) = 42 meters?

Why not?  What about the skin depth of the earth's surface?  "Skin
effect" has no useful relation to the current distribution in the human
body.  The dielectric constant of the water which comprises most of our
bodies does.

Ed

```