Message from discussion Doubleplusgood - first impressions

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From: Andrew McKenna <NOcmorSPAM3...@NObigpond.SPAMnet.au>
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Subject: Re: Doubleplusgood - first impressions
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Date: Mon, 19 Feb 2007 04:48:14 GMT
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Iain Chalmers wrote:

>> Watch out for lightning strike!
>>
>> -- 
>> Cheers
>>
>> Andrew
>>
>> (Make a lightning rod by gluing a blunt ferrous rod to the top of the 
>> motorcycle helmet, attaching a 4 metre length of copper strap to the rod 
>> with copper wire, and attaching a suitable boat anchor to the free end 
>> of the strap to make sure it stays earthed - any Windows 98 computer 
>> would do.)
> 
> A _blunt_ rod? Have you been taking physics lessons from Hamish again?
> 
> big
> 
"     Calculations of the relative strengths of the electric fields 
above similarly exposed sharp and blunt rods show that although the 
fields, prior to any emissions, are much stronger at the tip of a sharp 
rod, they decrease more rapidly with distance. As a result, at a few 
centimeters above the tip of a 20-mm-diameter blunt rod, the strength of 
the field is greater than that over an otherwise similar, sharper rod at 
the same height. Since the field strength at the tip of a sharpened rod 
tends to be limited by the easy formation of ions in the surrounding 
air, the field strengths over blunt rods can be much stronger than those 
at distances greater than 1 cm over sharper ones.
     The results of this study suggest that moderately blunt metal rods 
(with tip height–to–tip radius of curvature ratios of about 680:1) are 
better lightning strike receptors than are sharper rods or very blunt 
ones. "

C. B. Moore, William Rison, James Mathis, and Graydon Aulich, "Lightning 
Rod Improvement Studies". Journal of Applied Meteorology: Vol. 39, No. 
5, pp. 593–609. Langmuir Laboratory for Atmospheric Research, New Mexico 
Institute of Mining and Technology, Socorro, New Mexico. April 10, 1999.

Extracted from that authoritative source Wikipedia: 
http://en.wikipedia.org/wiki/Lightning_rod

-- 
Cheers

Andrew