Re: Experiment - Displacement Current's Magnetic Fields

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Original poster: "harvey norris by way of Terry Fritz <twftesla-at-qwest-dot-net>" <harvich-at-yahoo-dot-com>


--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Paul Nicholson by way of Terry
> Fritz <twftesla-at-qwest-dot-net>"
> <paul-at-abelian.demon.co.uk>
> 
> Hi Terry,
> 
> > I guess one could look at the "invention" of dD/dT
> as a great
> > theoretical leap, or a kludge to make the darn
> thing work ;-))
> 
> A fair description.  Picture yourself as a 19th
> century scientist
> trying to make sense of electricity and magnetism.
> They are each
> described separately by Coulombs law and
> Biot-Savart, and you know
> they are somehow connected because you have also
> have Faraday's and
> Ampere's laws.  You have an 'action-at-a-distance'
> description of
> gravity and static electricity based on a 'force
> field', ie the force
> that a test particle experiences (presumably
> instantly) in response to
> the 'source' of the field.  You desire a similar
> thing for B too.  You
> know it must be a vector because it has to describe
> the force on a
> test charge.  And you know that B must somehow
> satisfy Ampere's law.
> So you invent a B field vector and use it to
> describe Faraday's law,
> etc, fine. But when you come to look for a
> mathematical description of
> Ampere's law, you hit a big snag.  You find you
> cannot get a self-
> consistent mathematical description of this law.  It
> offers two or
> more different values for the voltage induced in a
> wire, depending on
> which surface you integrate the field across.  This
> was the famous
> 19th century crisis in electromagnetism.
> 
> Maxwell was motivated to plug in a dD/dt term
> because it gave the
> simplest bit of math which described Ampere's law
> and it still worked
> for the other stuff.  The requirement was a
> self-consistent description
> of Ampere's law, that's all.  Maxwell will have also
> noticed that
> putting this term in made the description of
> Ampere's law identical in
> form to Faraday's law, which was also pretty neat.
> 
In the
early 90's I purchased another Physics text,(Physics
for Scientists and Engineers) in which the following
is noted on pg 654;

We have named B the magnetic field and H the magnetic
intensity. These names are not universal. Sometimes B
is called the magnetic flux density and H is called
the magnetic field. Admittedly, the terminology is
confusing, and universal adoption of a single set of
terminology is unlikely in the near future.
Fortunately, the usage of the symbols B and H as we
have defined them is nearly universal. Thus the
calculation of a magnetic force on a moving charge or
a current nearly always involves B; similarly H is the
appropriate field in Ampere's Law.

It has cost me a bit of time to try and understand
that thing with Amperes law, as I did not pay
attention then, and integrals need that concept of
summation. I think it can be summed up by guessing
that a linear relationship is made between the amount
of magnetic field B obtained at a certain distance r
away from a conductor of i current. This becomes a
ratio, where a constant is derived. That constant is
known as the permeability of free space,mu(0) or k
determined by the equation (B)(2*pi*r)=k*i

What it seems to be (very confusing)is that B/H= the
permeability
constant k,(also?) which of course also changes with
core
material. I am unsure whether this is all of the
story, but I think it is  basically correct. HDN

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