Natural Science Forum / Physics / Electromagnetism / April 2004

I have a mathematical question about a problem from electromagnetic theory.
In electromagnetics, the surface current I(x) on a straight wire (dipole
antenna) due to, for example a coaxial feed, or an incident plane wave
follows from

Does anyone have a clue concerning the feedback(regeneration) coil of
this antenna design. I'm at a loss as to whether the feedback coil
should be a replica of the main coil, or some fraction there of, and
how it is coupled to the main coil. Please help!

I'm an electrical engineer with very basic knowledge in physics. I am
using 2.4GHz spread spectrum (frequency hopping) radios to transmit
data. I am trying to understand the effect of antenna height on
transmission distance.

does anyone have a good feeling for how a potential (or current) wave
propagates along a conductor? suppose for instance, you apply an ac
potential to one end of a conductor. the potential waveform propagates
along the conductor at some speed... the speed of light? also, what

I'm thinking about trying to build my own Hall probe, just for kicks.
But can anyone advise me on the best (and cheapest, if different!)
place in the UK to buy the Hall effect device?

On or about 16 Mar 2004 06:04:58 -0800
mg_weber@yahoo.com (mike) wrote in
<26578faf.0403160604.2494ab7a@posting.google.com>

Forgot the m in the "grad m" formula.
Grad m = (i Dm/Dvx + j Dm/Dvy + k Dm/Dvz)

Eexactly what is gauge?? I've read all the guff about the different ways to
get potentials out of Maxwell's field equations, but where does the name
'gauge' fit in?? Is it a size issue due to constants of integration? Where
does the name 'gauge' fit in is what I really want to know.

   I am using Ansoft's Maxwell 3D for the first time and I am trying to
figure out  how this program works. I implemented a simple
inhomogeneous model: a box containg another box, that contains a
smaller box. I assigned the source to the smallest box and then

If P is the electric scalar and A the magnetic vector potential, in
Lorentz gauge, then they satisfy the equations (Gaussian units)
De P - 1/c^2 d^2 P / dt^2 = - 4 Pi p
De A - 1/c^2 d^2 A / dt^2 = - 4 Pi J / c

I'm trying to derive the conservation theorem for electromagnetic
angular momentum, but I fail because there is a term I can't get rid
of.
Following Leonard Eyges in "The Classical Electromagnetic field"

   I am using Ansoft's Maxwell 3D for the first time and I am trying to
figure out  how this program works. I implemented a simple
inhomogeneous model: a box containg another box, that contains a
smaller box. I assigned the source to the smallest box and then

Evanescent modes play an important role in mode matching method of field
analysis at discontinuities e.g. between coaxial line and wave guide.
However, evanescent modes are obtained from an arbitrarily chosen
complex wave description. They are just fictitious components. The

Has anyone got a nice, accurate subroutine for evaluating the function
w(z), a complex error function with complex argument, defined in
Abramowitz and Stegun section 7.1.3?
TIA

My name is Derek Shaw and I am a highschool physics student (I hope this is
the right place for my question). I am looking to build some intrusting
project (eg a rail gun/tesla coil (too hard to build)). So what I want to do
is build a Thompson's Coil. Can anyone suggest a web page ...