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Re: sparks

At 17:45 2/18/01 -0800, Larry Woolf wrote:
According to the EB, the field strength for electrical breakdown of air at
atmospheric pressure is 10,000 V/cm. Within thunderclouds, fields of 1000
V/cm are exceeded only over limited areas. This information is also
available in the CRC Handbook in the spark gap section.

At 5:46 AM -0800 2/18/2001, John S. Denker wrote:
At 02:23 AM 2/18/01 -0800, Bernard G. Cleyet was skeptical of my guestimate
of the breakdown field:
It's about 3 megavolts per meter.


Here are some values from a table of Sphere-gap Spark-over Crest Voltages
Table 4.92 Ref 1
Sphere diameter 6.25cm 12.5cm 25cm
spacing
1cm 31.3kv 31.7
2.5 68.8/69.3 70.8 72
5.0 105.5 127.0/132.3 136
10.0 *192.0 241/253

Error +- 3% except *

You can see that for small gaps and large electrode diameters
in Summer at sea-level,
the breakdown field strength exceeds 3 MV/m
and for larger gaps it is not quite 2 MV/m

Where two figures are given, the breakdown for a negative crest is
given first, then a postive crest value

Ref: sec 4-586 Standard Handbook for Electrical Eng.
Knowlton, McGraw-Hill (25degC, 760mmHg)
brian whatcott <inet@intellisys.net> Altus OK
Eureka!