Re: is the magnetic field really moving?

On Tue, 26 Aug 2008 08:31:23 +1000 Timo Nieminen <timo@[EMAIL PROTECTED]
>
wrote:
| On Mon, 25 Aug 2008, Salmon Egg wrote:
| 
|> After reading all the posts here on this subject, I do not expect to 
|> find any more insight. Before throwing in the towel, I will try asking
a 
|> question once more.
|> 
|> Given a uniform and circularly symmetric cylindrical bar/disk magnet 
|> spinning on it axis, how can the rotation of the magnet be detected by 
|> observing properties of the magnetic field alone?
| 
| This is an entirely different question from ones about whether the field

| moves/rotates.
| 
| For small v^2/c^2, the magnetic field is the same for the rotating and 
| stationary magnet, so, strictly speaking, the rotation can't be detected

| from observing properties of the magnetic field alone.
| 
| Why restrict it to the magnetic field only? The rotating permanent
magnet 
| is covered well in Van Bladel, Relativity and engineering, pp 296-298. A

| unipolar generator uses the electromagnetic field to detect the rotation

| quite well indeed.
| 
| What kind of insight were you hoping for? The various phenomena are 
| well-described by existing theory - the electromagnetics of rotating 
| media is known (but isn't covered in many books).

I believe his question is equivalent to the question of whether a
conductor
that is in motion through space can tell whether the magnetic field that
is
crossing it perpendicular to its motion is there as a result of a very
long
magnet (imagine billions and billions of bar magnets attached side by
side)
that it is moving beside, or the result of a single magnet that is moving
with the conductor.  In both of these cases, the field intensity would be
the same for the conductor over the time of its movement.  If this
conductor
is perpendicular to both the vector of movement and the orientation of the
field, will a charge be induced in both cases?

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