Natural Science Forum / Physics / Electromagnetism / June 2007

Given E=a_r*(20/r^2) mV/m in free space, find rho_v (the volume charge
density) at the point (3,-4,1) cm
The answer is supposed to be -1.42 nC/m^3. I have tried Gauss's law
both in integral and differential form, but I do not get the correct

the best!  They allow you
to live forever:
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I think I once heard someone say that in theory,  an LNA with a power
MATCHED input (i.e. a high return loss) that the best THEORETICAL
noise figure that can be obtained is 3dB.  This is for the special
case of devices operated at room temperature, this discussion is not

Here's a typical "Radium" question for you:
Does anyone know of any experimental evidence giving the direct
observation of radio waves consisting of "photons"?
What I mean is it is well known that light frequency waves are not

Inside the hydrogen atom photon substructure known via self-field
theory introduces no new physics beyond that given by quantum
mechanics. Within molecules however, photon substructure introduces a
previously unknown quantum number by which molecular bonds can range

Does anyone out there know if this is possible or is this just a
crock? I've never heard of anything that could repel lightning! See
what I'm talking about here: http://www.matchrockets.com/earth/lightning.html.
Thanks in advance,

I want to learn, in-depth, the Maxwell equations. Any suggestions on
books, resource materials. I'm starting from scratch (know single
variable calculus, basic electrical theory). Thanks

Dears
I'm developing a big mag-core for an alterating magnetic field,100kHz／
150Gs, The problem now  is the terrible mag-loss inside the ferrite
magnet poles, with the shape 10cm*20cm*30cm, and are wound by the

This is essentially the same question I posted in the thread on "FM
Photons", and I've just become more puzzled (and I haven't seen any
replies there).  Very simply, if I have a source (a "carrier") of
monochromatic photons (at 800kHz, or at visible light - it's not

  I have in mind some interesting and relatively
simple experiments regarding electromagnetic induction.
The purpose is to reach a better understanding of the
very basics.

I read an article yesterday.  It talked about scientists transmitting
energy wirelessly by using some kind of electromagnetic resonance.  Here
is a link to the article:
http://news.bbc.co.uk/2/hi/technology/6725955.stm

The Pentagon and the U.S. intelligence agencies known as the N.S.A. [
National Security Agency ], C.S.S. [ Central Security Service ], D.I.A. [
Defense Intelligence Agency ], and the C.I.A. [ Central Intelligence
Agency ], have extremely top secret technology which can pick up ...

I just read a text that said that a microwave oven
contains voltage at about 5kV - at high current, and
that CRTs have 35kV - at low current. Thus, the
microwave oven is more dangerous because of

The surface of a mirror usually
is metal plated. How does the
surface reflect (bounce back)
a photon. If the photon bounces back

What does the electric field of a uniformly increasing magnetic field
look like? Placing a charge at each point and measuring the force on
it would be one way to measure the E, yet why would it move in a
particular direction normal to B given the symmetry of the problem?