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Re: Tesla Coil RF Transmitter

Original poster: stork <stork@xxxxxxxxxxxxxxxxxxx>

Hi Steve,

A side from your reference to displacement current producing a magnetic field, I don't think we need to revisit that thread again again at this point. Besides no one can measure any magnetic field produced by "displacement current" in a dielectric.

So I'll point out why your Gedanken experiment fails.

The Maxwell equation you put forth is curl H= J+dD/dt. This equation requires an electrically closed loop circuit. Of course, there is no closed loop circuit in our experiment of longitudinally waving a macroscopically charged body back and forth. This particular equation cannot meet the experiment, let alone confirm a magnetic field being produced by a varying electric field in a dielectric.

I suggest the more appropriate equations:

F = qE  or E = F/q



Regarding the falling battery.

BTW, a charged dry cell battery is a simple dipole. Electric field lines radiate out from the positive pole, curve around and enter the negative pole.

If one arbitrarily draws a surface line around the battery (if 3D, a volume line) at any instant when the battery is stationary or falling under the force of gravity, the net charge from the dipole inside the circle or bag is zero. The chosen surface line can be any size or form.

Gauss's law states:

  INTG E.dA = 0 (when zero net charges are inside the surface.)

The net charge over the entire surface integrates to zero when the inside net charge is zero.

Or, net flux over the entire surface integrates to zero.

So if, there is zero net charge or zero net flux on the selected Gaussian surface around the enclosed dipole then there is no net E field and certainly no H field produced.



Stork







Original poster: Steve Conner <steve@xxxxxxxxxxxx>
 > "In this electrostatic event energy is
 > surely transferred
 > without the benefit of a magnetic field or current.
 > If you see it
 > otherwise, please produce the experiment."
This is a Gedanken experiment :P I thought about it
some more, and I guess that physically moving a
charged body is similar to charging and discharging a
fixed capacitor. After all when you move the body,
even though the charge on the body stays constant, the
E-field seen by surrounding objects will change since
the geometry of the system has changed.
So, I hope we agree the moving body creates a
time-varying E-field. Then, if you believe Maxwell's
equations- the relevant one being
curl H= J+dD/dt
the time-varying E-field (the dD/dt term) creates a
displacement current and this current gives rise to a
magnetic field. Then, any mechanical work done on
surrounding objects by "electrostatic"
attraction/repulsion must be accounted for by E x H.
I bet that if you do all the math, the energy balance
will add up. We have all seen the experiment where
styrofoam packing peanuts or pie dishes get launched
from the terminal of a HV DC power supply. If I drew a
control surface around one of those peanuts in
mid-flight, and calculated the integral of the
Poynting vector over the surface, I would expect to
find an inward EM power flow that equalled the
mechanical power lifting and accelerating the peanut.
That's how my argument goes. To be honest, I am
starting from the biased viewpoint that Maxwell's
equations are valid and power can't be transmitted by
pure E or H fields- wherever you have power, there
must be both E and H. So I invite you to put forward a
counter argument.

 > Do you really think tossing a dipole battery with
 > positive and
 > negative poles and equal but opposite charges out a
 > window can create
 > a radio wave?
As long as the positive and negative poles are
separated by a non-zero distance (ie the battery has a
finite size) it should work as the EM effects of the
two ends won't exactly cancel. If it spins as it
falls, so much the better :)
Steve
http://www.scopeboy.com/

.