Re: Formula for self C of a Coil (not Medhurst)

• To: tesla-at-pupman-dot-com
• Subject: Re: Formula for self C of a Coil (not Medhurst)
• From: "Jan Florian Wagner" <jwagner-at-cc.hut.fi> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Tue, 25 Apr 2000 18:31:31 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi,

> Does anybody have the formula or a link for the capacitance of an isolated
> cylinder that is not due to Medhurst?
> My suspicion is that the Medhurst formula is incorrect or it contains a
> fiddle factor.

Just correct me if I'm wrong, but I heared/read that Medhurst derived the
"self capacitance" and its formula from experiments he made - he 
calculated the coil inductance and then measured its self resonant
frequency. From these values he dervied a theoretical value for "self
capacitance", the theoretical capacitance that would together with an
ideal inductor give exactly that resonant freq. Doing lot's of experiments
with different sized coils, he made up the table and formula.

So, how far is the "self capacitance" from the "true" coil capacitance
anyway? Is there a way to determine the "true" capacitance at all?
I mean, an LCR meter probably doesn't help much as they just measure the
impedance at some freq, so the output value would be an inseparable L & C
combination...

greetz,
Jan

--
*************************************************
 Jan Florian Wagner
 http://www.hut.fi/~jwagner

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