# RE: K Factor & Mutual Inductance

Subject:
RE: K Factor & Mutual Inductance
Date:
Mon, 14 Apr 1997 03:35:05 +0000
From:
"John H. Couture" <couturejh-at-worldnet.att-dot-net>
To:
Tesla List <tesla-at-pupman-dot-com>

At 09:59 PM 4/13/97 +0000, you wrote:
>Subject:
>            RE: K Factor & Mutual Inductance
>       Date:
>            Mon, 14 Apr 1997 08:28:36 +1200
>       From:
>            "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>Organization:
>            Wellington Polytechnic, NZ
>         To:
>            tesla-at-pupman-dot-com
>
>
>John, all,
>
>>  Thank you for the derivation of Q = sqrt(L/C)/R.  I lost my Radiotron
>> years
>> ago (a good book). I did find the derivation in Henney's Radio
>> Engineering
>> Handbook.
>> The sqrt(L/C) is shown in my TC Notebook to calculate the secondary
>> circuit
>> peak current. This is the equivalent of Zo in Ohms law. The Zo and Xo
>> are
>> consudered almost equal for these calculations.
>>
>> Apparently we both agree that the R is not the DC or AC resistance. It
>> must
>> be determined by calcs after finding the Q and the X of the coil.
>
>Whoa! It is the resistance at the frequency of interest (effective
>AC resistance). The rho of the material is factored in. The only
>reason it is difficult to calculate is the many-bodied problem. The
>surroundings affect it. You can test this for yourself. Try mounting
>a primary and cap close to ground and measure its Q without the gap.
>Then sit it up a few feet and measure again. This should be of
>interest to anybody wanting to couple more primary power to the
>secondary than ground etc.  You can also see the effect of doing this
>on the secondary.
>
>Malcolm
>
>---------------------------------------------------

Malcolm -

I assume when you say "the rho (a greek letter) of the material" you
mean
the resistivity of the material. Or are you using some other equation.

When you say "reason it is difficult to calculate" what equations are
you
using?

I am working on a graph for effective resistance. Do you have any
suggestions?

John Couture