Capacitance of a long thin rod (e.g. a spark) (fwd)

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• Subject: Capacitance of a long thin rod (e.g. a spark) (fwd)
• From: Tesla List <mod1-at-pupman-dot-com>
• Date: Wed, 15 Jul 1998 21:44:56 -0600 (MDT)
• Approved: mod1-at-pupman-dot-com

---------- Forwarded message ----------
Date: Wed, 15 Jul 1998 10:15:39 -0700
From: Jim Lux <James.P.Lux-at-jpl.nasa.gov>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Capacitance of a long thin rod (e.g. a spark)

An equation you may find handy for addressing the issue of the change in
capacitance (and hence resonant frequency) of the secondary due to a
spark emerging from the top is:

	C = 2 * pi* epsilon0 *length / ln(length/radius)
	  = .555 * length (cm) / ln(length/radius) pF

For a 1 meter spark (100 cm) with a radius of .01 cm, the capacitance
is:

	= .555 * 100 / ln (100/.01) = 55.5/9.2 = 6 pF

This is a pretty significant change out of a total secondary C of 50 pF
or so.... (a 5% change in frequency)

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