Re: rotating magnetic field

On Thu, 04 Jun 2009 23:24:30 -0700 Salmon Egg <SalmonEgg@xxxxxxxxxxxxx> wrote:
| It looks like we have another Benj on our hands.
|
| In article <h0a4qd013kh@xxxxxxxxxxxxxxxxx>, phil-news-nospam@xxxxxxxx
| wrote:
|
|> On Wed, 03 Jun 2009 22:30:53 -0700 Salmon Egg <SalmonEgg@xxxxxxxxxxxxx>
|> wrote:
|>
|> | It seems like this topic will replace perpetual motion
|> |
|> | Consider a solenoid powered by small battery attached to it.
|> |
|> | 1. Rotate the solenoid about its rotational symmetric axis. Does the
|> | field rotate as you rotate the solenoid. I say no because the field is
|> | the same before and after a rotation, Any time derivative of a magnetic
|> | field is going to be zero, NOTHING CHANGES!
|>
|> You are only measuring one aspect of the field. With a symmetrically
|> uniform field, no density change takes place in rotation. If it did,
|> any crossing wire would experience that field density change and have
|> an alternating voltage/current induced.
|
| What am I missing? For nonrelativistic speeds what else is there to a
| magnetic field other than a vector function that gives the magnitude and
| direction off the magnetic field as a function of position and time?
| This function is subject to restrictions described by Maxwell's
| equations, namely div B =0. Give me evidence instead of assertion.

First you need to admit that you are missing something. Asking is a step
in that direction. What to think about ... how is it that some other mass
can have motion _relative_ to a magnet _and_ be affected by that magnet
when the orientation of that relative motion is not resulting in a change
of the magnitude and direction of the magnet.

I'm not sure what it is that makes this work. The idea that the field is
rotating is merely a _perception_ of the effect. But the effect is that if
the magnet itself is rotating (rotation axis in line with field axis) then
there is a voltage in conductors that are at right angle to both the axis
and the direction of rotation at the particular radial point where that
conductor is.

I speculate that perhaps the spin alignment of the atoms of the magnet is
in fact making a field that has a characteristic spin, even when the magnet
is not rotating. Then when it does rotate, somehow that spin is modulated.
This is one of the answers I seek. But I seek it because I know that when
the magnet rotates, it changes the field, or the effect of the field, in a
corresponding way. Someone who denies such changes might not be seeking
the why of this.


|> | 2. Rotate the solenoid about a two-fold axis. The magnetic field for
|> | this does rotate. t least the magnetic field configuration changes. You
|> | now can have nonzero derivatives of field components because these
|> | components will now differ during from one instant to the next.
|>
|> The dominating effect here is the changing field density. Rotation does also
|> exist, but it isn't a rotation that can induce a smooth direct
|> voltage/current.
|
| The "changing magnetic field density" by itself is good enough for me. I
| have no religious drive to call it rotation.

The change will differ based on the direction and speed of the rotation.


|> | That is all there is to it. Do not try to read more into it than there
|> | is.
|>
|> There is more to it than that.
|>
|> A magnetic field has atomic spin character to it. The field "exists" when
|> all the spins are in alignment. The rotation first described is in the same
|> orientation as these spins. It is, in effect, a modulation of the spin. Or
|> the spin is a modulation of the rotation ... however you want to look at it.
|
| There are no spins in a vacuum although there can be magnetic fields.
| Spin is a red herring here.

If you believe there is truly nothing in a vacuum, then how can you believe
there can even be a magnetic field in a vacuum.

My belief is that all matter has no finite boundary. We merely perceive such
a boundary on the basis of limits of space occupancy sharing that mass exhibits
under certain conditions. You cannot pass your hand through the wall despite
the fact that based on how tightly atoms and particles _could_ be packed given
sufficient pressure, your hand and the wall are very sparse masses and mostly
consist of empty space between what we think of as atom boundaries.

The particles merely have a central point. They extend infinitely in all
directions, with all mass effectively overlapping. This extension is not
significant enough to prevent other atoms from being present. But when a lot
of particles are close together (as in an atomic nucleii, or many atoms in an
object) there is an accumulation of their extended space existance. It's still
not much on the macro scale of our nake eye observations. At the atomic level
the effect is significant with respect to inter-atom effects.

The extension exhibits the particle's spin. When sufficient particles have a
spin with the same or nearly same orientation, as in a magnetic with most of
its domains oriented the same way, then we see a "field" we call a magnetic
field. What you (also) have is the extension of these particles with a common
spin alignment extending through space infinitely. When the spin orientations
are all a random jumbled mix, the vector sum is near zero. But when they are
all in the same common alignment, the vector sum can be significant. Stack on
a second magnet (in the same orientation) and the field gets even stronger.

To me, there is no such thing as empty space. Instead, there is a region of
freedom where the particles' own motions overcome the effect of the extension
of other particles.


|> One misconception of a magnetic field that lots of people have is that they
|> believe it is something intrinsic to the space where the field is sensed.
|> But in fact, a field is an extension of the magnet itself. Or more
|> accurately
|> it is an extension of each atom or particle of that magnet, summed together
|> with a non-zero orientation.
|>
|> If a magnetic field can exist independent of the motion of the magnet that is
|> its source, then this creates a physical contradiction in certain setups of
|> magnets, conductors, and motion. In particular, a configuration can be made
|> that has a conductor loop with the field intersecting with that wire in the
|> same direction all the way around the loop. This configuration will have the
|> conductor entirely in one plane. The field is radial along that plane and
|> has
|> a return path off the plane. Motion of this complete assembly in a direction
|> perpendicular to the plane should induce a current in the conductor loop if
|> the field motion is not a factor. After all, each point in the conductor
|> loop
|> is in a field oriented at one angle, with the conductor direction at a right
|> angle to the field, and with motion in the remaining right angle. But this
|> will fail to induce electricity because there is no motion _relative_ to the
|> magnetic field.
|
| Please reformulate these notions. Before I can contemplate the physics,
| I have to understand the English that describes the configuration.

We might be better off with another language. English is very poor at this.
Even words are in general, so a verbal description in any language is likely
to be difficult to understand. When I find the tools I need to make pictures,
I believe that will help.

I'll try giving some more details, even if this might be a futile attempt.

A magnet is formed in the shape of a ring. The orientation of the magnetic
poles is radial. That is, the N-pole faces away from the center of the ring
while the S-pole faces inward toward the center. The model of lines of flux
when applied here would have a donut shaped loop of flux lines on each side
of the magnet (a side where viewing the ring lets you see its circularity or
radius).

Now consider TWO such ring shape magnets, where the inside radius of the
larger one is larger than the outside radius of the smaller one. When these
rings are placed on the same plane, with their center's at the same point,
the smaller one is "inside" the larger one. Both ring magnets have N-pole
facing outward and S-pole facing inward. Now the lines of flux _between_
the magnets will follow a nearly straight line from one to the other (there
will be a slight bowing of these lines). There will also be the "return"
line extending outward from the outer magnet, bending around back toward the
center (half going to one side and half to the other side). These return
lines go back to the inner S-pole side of the inner magnet.

The conductor loop is run around the space between the two ring magnets. So
it is at a right angle to the magnetic field. Now if you face one side of
this assembly, you see one ring magnet, then around it a loop of conductors,
and around that a larger ring magnet. Move the whole assembly in the direction
a side faces (toward or away from you). Now you have a field at one angle, a
conductor at a right angle, and motion at a right angle to both of those.

You can get free motion of this whole assembly by facing the sides east and
west and let the Earth do it for you. Of course, if this were to work and
let you extract power/energy from this motion, that would have to mechanically
work against the motion, so it would need to be rigidly attached to the Earth
to avoid flying off in some direction.

And if this were to work, you could just spin it's angle around to find the
vector sum of all the various directions of motion your point on the Earth is
currently in.

Even though this is not a case of rotation, per se, it is an example of how
merely having motion of a conductor in a field, where the field is also in
synchronous motion (same direction and velocity), yields no electrical
potential or current. The case of rotating one or two disk magnets and a
disk conductor in a way like Faraday's experiment (a disk magnet to ensure
the field is uniform around the axis) is simply a case of (lack of) relative
motion. Cut a hole in the center of the disks in Faraday's experiement so
you have rings instead (though unlike the description I gave above, this
leaves you with rings with the poles facing to the sides) and consider only
where the disks exist (away from the axis) and it will be more easily seen
that it is all about motion, and not rotation per se. It just happens that
this motion is rotational.

So the question "does the magnetic field rotation with the rotating magnet"
is essentially the same as the question "does the magnetic field move with
the motion of the magnet" (even if that motion is around a circular path).

My answer is "yes".

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