Re: magnetic field
softh_at_bellsouth.net
Date: 09/27/04
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Date: Mon, 27 Sep 2004 11:36:17 GMT
On Mon, 27 Sep 2004 03:13:03 UTC, Sylvia Else
<sylvia@not.at.this.address> wrote:
>
>
> Kevin Kilzer wrote:
>
> > On Sun, 26 Sep 2004 18:53:21 -0400, "Ken" <lera@sympatico.ca> wrote:
> >
> >
> >>I would like to know what is a magnetic field. I mean what is it composed
> >>of.
> >>I searched google , asked people around me , no one seems to know.
> >>Obviously everyone knows where how, but not what.
> >>I thought it was electrons, but that cant be.
> >
> >
> > Basically, both electric and magnetic fields store electromagnetic
> > enegy. Electric fields can be created by something as simple as a
> > battery, and magnetic fields come from magnets or from electrical
> > coils while a current flows. Why magnets make magnetic fields is a
> > question for quantum physics.
> >
> > With respect to Sylvia, James Clerk Maxwell expressed a relationship
> > between electric and magnetic fields in the mid 1800's. Maxwell's
> > contribution was to show that a magnetic field is created as an
> > electric field changes, and an electric field is created as a magnetic
> > field changes. The result is that if I switch an electric field off
> > and on, I get a magnetic field that swells and collapses with each
> > on-off transistion.
> >
> > If I flip the swith fast enough at some frequency, I will find that
> > the magnetic field comes and goes with the same frequency. But, since
> > a changing magnetic field will create its own electric field, the
> > effect moves out to this new field, which makes another magnetic
> > field, and so on, and that is radio.
> >
> > Kevin
> >
>
> I'm not disagreeing with Kevin, but there is a simple thought experiment
> that shows how careful one must be about taking a theory, such as that
> of James Clerk Maxwell, and attempting to use it as anything more than a
> description.
>
> Take two electrons, separated in space, stationary relative to some
> observer. There's an electric field, obviously, but no magnetic field.
> Now take another observer moving perpendicularly to the line joining the
> electrons. This observe sees the electrons in motion. Electrons in
> motion are an electric current, and an electric current produces a
> magnetic field, so for that observer there is a magnetic field present.
>
> So one observer finds a magnetic field present where another observer
> finds none. The notion that a magnetic field has a concrete existence is
> clearly problematic. This paradox doesn't appear in the theory itself,
> because it simply tells you what will happen (or more exactly, what your
> measurements will show). It doesn't say anything about what is "really"
> there.
>
> Sylvia.
>
Hi Sylvia,
Just a little note here, in your post the observer is moving relative
to the electrons not the electrons relative to each other so there is
no change in the electric potentials, unless the observer is at a
different electrical potential themselves, of course then they are not
a 'neutral observer" so the stationary observer would then see the
field created as the other non stationary observer moved past the
stationary electrons. The question I come up with is exactly what does
the "at differential" moving observer see, since they are part of the
emf/cemf event.
Matt
-- "It's not what folks don't know that gets 'em in the most trouble, it's the things they do know that ain't so" Will Rodgers "Any sufficiently advanced technology appears as magic" Arthur C. Clarke
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