[net.general] Speed of electricity summary

will@sdchema.UUCP (07/10/83)

Since the amount of responses coming in to the 'speed of electricity'
question has slowed to a trickle, I am posting two responses that were
most complete.  The first, if not true, should prove interesting.  I
take no responsibility for these responses and their content.


From: cbosgd!res (Robert Stampfli)

Electromotive force will propagate in a wire at about the speed of light,
which is 3E8 m/sec or 186,282 mph. Of course, the speed of the actual
electrons through the wire is much slower. It is sort of like a tube
full of ping-pong balls: You can push one in one end, and another will
pop out the other almost (but not quite) immediately, but the speed of the
actual ping-pong balls is not particularly fast. You can figure out how
long it takes for an electromotive impulse to cross the country. I think
it will circle the globe about 25 times in a second. However, a bolt of
lightning is a mass of electrons, and therefore propagates much more
slowly. I have read, but don't remember just how fast a typical lightning
bolt propagates through the atmosphere. However, once the path between
the cloud and ground is made, the electromotive force (but not the 
electrons) moves at close to the speed of light.


From sdcsvax!ihnp4!burl!spanky!hocda!houxm!houxz!halle1 Mon Jun 27 09:08:53 1983

Assuming nominal dispersion, the speed of electricity, ie the speed at which
the electric field propagates, is the speed of light.  (Actually, it is
exactly the speed of light, taking into account the index of refraction.)
This means it travels about a foot a nanosecond (1.0 E-9).  Obviously it takes
a year to go a light year.  Radio waves and electrivity are both
like light.  If their indeces are the same, they will have the same velocity.
BEWARE, however, in electrical circuits, there are many things that could
increase the dispersive index, slowing down the propagation, so the only
correct answer would involve knowing the medium.