Re: impedance of free space

["Bob Sciamanda" <trebor@velocity.net>]

The ratio of E (volts/meter) and H(amperes/meter) has units of
volts/ampere = ohms!
In a plane wave in free space this ratio =sqrt(mu/epsilon)[o] = 376.6
ohms.  The value of this ratio (impedance) in a medium supporting E&M
propagation is a useful characterization of that medium; in general Z is
a complex number and carries phase information (Evs H), just as its AC
circuit analog.

-Bob

Bob Sciamanda   trebor@velocity.net
Dept of Physics
Edinboro Univ of PA  http://www.velocity.net/~trebor
Edinboro, PA   (814)838-7185
-----Original Message-----
From: Larry Smith <Larry.Smith@snow.edu>
To: PHYS-L@atlantis.uwf.edu <PHYS-L@atlantis.uwf.edu>
Date: Wednesday, April 22, 1998 6:24 PM
Subject: impedance of free space


> Sorry if this is a stupid question, but I'm rusty on this and none of
the
> H&R or Serway level books give me a good answer.  My students asked, "If
> free space is totally empty, why does it have impedance [of 377 ohms]?"
I
> was about to answer that free space isn't really empty and launch into
> something about a sea of virtual particles, but then I thought I'd
better
> ask the list first.
>
> Thanks in advance,
> Larry