Xref: utzoo rec.boats:4151 sci.physics:13694 sci.electronics:13021
Path: utzoo!utgpu!watserv1!watmath!att!oucsace!bwhite
From: bwhite@oucsace.cs.OHIOU.EDU (Bill White)
Newsgroups: rec.boats,sci.physics,sci.electronics
Subject: Re: St Elmo's Fire (was Re: Lightning)
Keywords: Induction, space charge, capacitance, and bulldrops ?
Message-ID: <1584@oucsace.cs.OHIOU.EDU>
Date: 22 Jul 90 06:34:34 GMT
References: <2436@speedy.mcnc.org> <1990Jul19.210925.165@mlb.semi.harris.com> <2438@speedy.mcnc.org>
Followup-To: rec.boats
Organization: Ohio U, home of the mighty Hocking River!
Lines: 51

In article <2438@speedy.mcnc.org> kgreer@mcnc.org.UUCP (Ken Greer) writes:
>In article <1990Jul19.210925.165@mlb.semi.harris.com> sjohnson@gumbee.mlb.semi.harris.com (Scott Johnson) writes:
>>In article <2436@speedy.mcnc.org> kgreer@mcnc.org.UUCP (Ken Greer) writes:
>>>In article <1990Jul18.111525.5749@ioe.lon.ac.uk> teexmmo@ioe.lon.ac.uk (Matthew Moore) writes:
>>>++I know this is the commonly accepted idea behind lightning rods, but as I
>>>++learned in my college physics class, lightning rods actually REPEL lightning,
>>>  Ok, so "knowing" all this, as I understand it to be said, one should be
>>>safer standing on the roof next to a lightning rod, instead of somewhere
>>>else?  Or do I completely miss the point?
>>Kim, I think they would tell you that this is a bad idea  [....]
>   My (not quite sarcastic enough) point also.  (See question below).
>
>>	and lightning STRIKES lightning rods!
>>        Thats how they protect a house, they deflect the current!
>>	Come on guys!
>
>  My only question now to those who *seem* to be saying it deflects
>lightning (assuming "deflecting" means away from the lightning rod):
>
>	Would you hold an umbrella (which is a lightning rod connected to
>	ground by the person holding it) up during a lightning storm?  I
>	think not.

	Well, I remember an article in some electronics magazine about
this subject.  It seems that yes, lightning rods can repel lightning, and
yes, lightning rods can also attract lightning.  It all depends on how
well the thing is grounded!  The big problem is, many lightning rods are
not really well grounded, and as such, what they really do is just pick up
the charge that's in the surrounding environment (read: the air).  The
article then stated that one of the best methods for lightning protection
was to erect a grid of metal pipes above a structure, and leave it
ungrounded.  It seems that the lightning would then avoid the structure
completely, as a like charge would be induced in the grid as the first
(invisible) stroke occurred.
	On the other hand, a well-grounded rod (for a really good ground,
you should have a bunch of "roots" coming off the ground rod in a star
pattern, and salt the whole thing with copper sulfate or equivalent) will
tend to attract lightning.
	Keep in mind that, yes, the difference in resistance can be minimal
when the voltages of lightning are considered.  But then again, so is
the difference in resistance between a flat open plain, and a person standing
on that plain.  But lightning _will_ find the path of least resistance, no
matter how little difference there is from the surrounding terrain.

	Of course, the best thing to do is just not build in open, high
terrain :-)

-- 
|   Bill White			Internet: bwhite@oucsace.cs.ohiou.edu	|
|	PAUL'S LAW:							|
|		You can't fall off the floor.				|