Re: Magnetic Field in a Flat Spiral

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve Greenfield by way of Terry Fritz <twftesla-at-qwest-dot-net>" <alienrelics-at-yahoo-dot-com>

How about suspending iron filings in oil in a small clear cube?
They should align with the field along their length, even in an AC
field.

I am very interested in what you find. Does anyone have software
that will simulate this? It'd be interesting to compare to what
David finds.

Steve Greenfield

--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "David Thomson by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>
> 
> The magnetic field of a flat spiral coil has an elongated torus
> shape near
> the surface of a flat spiral coil.
> 
> I've tried this experiment on single wound, bifilar wound, and
> wye coil
> wound flat spiral secondaries, with the same results for all.  A
> 12VAC 3A
> wall transformer was connected between the center tap and the
> outer lead.  A
> NIB disk magnet is held in the hands.
> 
> With the AC power on, hover the NIB magnet in various positions
> around the
> coil.  The magnet vibrates strongly, but has no magnetic pull in
> any
> particular direction.  But as the magnet is turned through the
> various axes
> in the hand it is found that at different locations over the coil
> the magnet
> vibrates noticeably stronger along some axes than it does others.
> 
> In the center of the coil, the position with the least vibration
> is when the
> N/S poles are perpendicular to the plane of the coil (x axis). 
> But as the
> magnet is brought further out, the point of least vibration
> occurs as the
> magnet becomes more perpendicular to the y axis (in a rotational
> coordinate
> system.)  So as the magnet travels toward the outer winding, the
> N/S poles
> are pointing toward the z axis (the z axis is up and down through
> the center
> of the coil.)
> 
> The magnetic field turns 90 degrees in a very short space near
> the outer
> windings and continues around to the bottom such that it is 180
> degrees from
> the upper magnetic field.  The magnetic fields above and below
> the coil are
> parallel to each other but pointed in opposite directions.  The
> magnetic
> field in the plane of the coil is pointing in the same direction
> as the
> field in the center of the coil, but in opposite directions.
> 
> I also noticed that when I did this experiment near a large
> ferrous object,
> the magnetic field around the space of the coil leaned in the
> direction of
> the ferrous object.
> 
> There are many other interesting geometric features of the
> magnetic field.
> 
> Has anybody on this list done research into the magnetic fields
> around coils
> in general?  I'd like to learn more about this.
> 
> Dave
> 
> 
> 


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