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From: levy@ttrdc.UUCP (Daniel R. Levy)
Newsgroups: net.sci
Subject: Re: Question about Electricity
Message-ID: <554@ttrdc.UUCP>
Date: Sat, 2-Nov-85 18:45:01 EST
Article-I.D.: ttrdc.554
Posted: Sat Nov  2 18:45:01 1985
Date-Received: Sun, 3-Nov-85 09:17:56 EST
References: <621@hlwpc.UUCP> <662@petrus.UUCP> <714@alberta.UUCP>
Distribution: net
Organization: AT&T, Computer Systems Division, Skokie, IL
Lines: 33

In article <714@alberta.UUCP>, makaren@alberta.UUCP (Darrell Makarenko) writes:
>
> I remember doing experiments in grade 12 science showing
> that pure water does not conduct electricity.  Salt water did conduct
> because of the Na+ and Cl- ions.  Of course air does not conduct
> electricity either but lightning still hits the ground.
> Question: Does pure water conduct electricity?  If it does not
> (as I believe) why does one have to be extra carefull about getting
> elecrocuted when standing in a puddle of water??

If you had tested tap water too you would have found it to be a pretty fair
conductor.  It doesn't take much impurities to do this.  You can pretty well
count on all naturally occurring water to have enough impurities to be a
good enough conductor to allow dangerous amounts of current to pass at house-
hold power voltages, given the usual small distance in the puddle between
your skin and a good conductor, namely the ground, at an opposite potential
to a "live" wire (since most electrical systems have one side of their voltage
source tied to an earth ground somewhere).  You touch the other side of the
voltage source while standing in such a puddle, and you get shocked or worse.

The lightning mechanism is different.  The voltage difference between cloud
and ground or cloud and cloud is sufficient to ionize the air, whereupon it
WILL conduct electricity (very simplistic explanation; the ionization occurs
in steplike stages) sort of like neon does in a neon lamp.  Now the question
of how the cloud achieves that voltage is a different one and I understand
there are several explanations (anyone care to elaborate?).
-- 
 -------------------------------    Disclaimer:  The views contained herein are
|       dan levy | yvel nad      |  my own and are not at all those of my em-
|         an engihacker @        |  ployer or the administrator of any computer
| at&t computer systems division |  upon which I may hack.
|        skokie, illinois        |
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