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From: leichter@yale-com.UUCP
Newsgroups: net.followup,net.micro,net.physics
Subject: Re: speed of electricity
Message-ID: <1677@yale-com.UUCP>
Date: Mon, 27-Jun-83 15:14:50 EDT
Article-I.D.: yale-com.1677
Posted: Mon Jun 27 15:14:50 1983
Date-Received: Mon, 27-Jun-83 23:32:36 EDT
Lines: 14

"The speed of electricity" is not a particularly meaningful term.  If you
ask "how fast do electrons move through a wire", the answer is "very slowly"
(a couple of feet per second, at most).  However, this is not a figure of
much interest.  A meaningful question is "How fast can a message be propagated?"
(where "message" is very general - it includes the the "message" that the
wall switch has been closed "telling" the light bulb to light up), the answer
to which is again complicated - because it depends on the exact circuitry -
but is something on the order of half the speed of light in a vacuum.  A
good rule of thumb is that light travels about a foot per nanosecond, so
electrical impulses in typical circuitry travel at about 6-8 inches or so
per nanosecond.  This works out to something like 1/100 of a second to
cross the US.
						-- Jerry
				decvax!yale-comix!leichter leichter@yale