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Re: Medhurst now empirical formulas

In a message dated 7/12/99 3:27:33 AM Central Daylight Time, tesla-at-pupman-dot-com 
writes:

<< Way back in the 1930's  >>

Bryan, Ed, Terry--all,

The 1930's were "only yesterday." :-((

Thanks for the Medhurst info and the QuickBasic file. This latest entry into 
the stupid
question contest has helped me because outside of the Tesla List I have never
seen the Wheeler and Medhurst names attached to the to the various empirical 
equations for the intrinsic inductance and capacitance of a solenoid.   	
						

 Terry writes that the other empirical equations are based on the Medhurst 
data. In Terman's Radio Engineering, 2nd ed., he shows a graph for 
determining the self inductance of a solenoid based on the ratio of H/D. 
Basically Wheeler, Terman graphs an
empirical constant, F, vs  the ratio of H / D for a range of 0.1 to 10.1 to 
solve the empirical
equation Lself = F x diam x N squared.

The Medhurst data can be found at 
www.peakpeak-dot-com/~terryf/tesla/misc/medhurst.jpg
Thanks Terry, one giant leap :-)). I graphed k vs the ratio of H / D for a 
range of 1.0 to 5.0
to solve the empirical equation for the intrinsic capacity of a solenoid: 
Cself = k x diam.
I find the graphs of greater value than the equations; can anyone explain how 
far one
can safely extrapolate before strange things happen?

In the appendix of Terman's second edition, there is an excellent discussion 
of various
empirical formulas for the intrinsic capacitance and inductance for all forms 
of coils including the toroid, and for many of the capacitance problems 
including
transmission lines and solenoids. 

Bryan writes: "Has anyone found the physical basis for the data?"

Terman is speaking specifically about the inductance equations but I think 
the statements
also apply to the empirical capacitance equations as well. Terman writes: 

"Skilled mathematicians have derived formulas that give the inductance of all 
the 
commonly used types of coils with non-magnetic cores in terms of the coil 
dimensions.
These formulas are usually both complicated and hard to derive because of the 
difficulty
encountered in calculating the magnetic flux produced by the current flowing 
in the coil.
In order to make such formulas of practical value, they are always simplified 
by the use of coefficients."

Well, that's good enuff for me, first things first, it's pool time!! :-))

The Tesla List is the greatest.
Ralph Zekelman