Re: Is electromagnetic field theory unified?

From: Bjoern Feuerbacher (feuerbac_at_thphys.uni-heidelberg.de)
Date: 02/21/05 

Date: Mon, 21 Feb 2005 14:02:02 +0100

JM Albuquerque wrote:
> "Franz Heymann" <notfranz.heymann@btopenworld.com> escreveu na mensagem
> news:cv9p9p$6m0$2@titan.btinternet.com...
>
>>"JM Albuquerque" <jm.aREM.OVE@sapo.pt> wrote in message
>>news:37q2i5F5fqjl5U1@individual.net...
>
>
>
> (snip)
>
>
>>>What I'm missing here is how a magnet radiates just because it is
>>>rotating, and the same magnet doesn't radiate when it is stopped.
>>
>>Because when it rotates about an axis perpendicular to its magnetic
>>axis it constitutes a magnetic field which, at any position, varies
>>periodically with time in both magnitude and direcrtion.
>
>
>
> Actually I'm not satisfied with your explanation.

Why not? Where exactly do you differ?

> The fact is that I can prove you that a stopped magnet also radiates.

Please do.

>>>So far I've seen no explanation and I can't see any logic. I've read
>>>your other posts and arguments.
>>
>>Then if youy do not see the explanation, you have some problems with
>>your cognitive system
>
>
> Not so.
> I do have a very good cognitive system.

Several people in this thread beg to differ.

> Its you that cannot explain why rotation causes radiation.

Because there are changing electromagnetic multipole moments. Where is
the problem?

> You suffer from the same problem most of the physicists suffer. To much
> mathematics and to little physics understanding, and that's what I'm going
> to prove here.

So far, you have only shown that you don't understand Maxwell's equations.

[snip]

>>>Where is the electric field?
>>
>>A time dependent magnetic dipole radiates.
>
>
> A stopped magnetic dipole also radiates!
>
> Before I prove you that a stopped magnet also radiates I have a question.
> Them I will nail you and finally I will conclude.
>
> You said that a rotating bar magnet radiates

Right.

> and that you can prove so by
> means of a receiving antenna, right?

Partly right. There are also a lot of other possibilities.

> Let us assume you place the antenna in short distance, 1 meter or so
> distance, OK?
>
> The new situation is the following:
> The same bar magnet is stopped on the top of a round table.
> The bar magnet is in the middle of the round table.
> The antenna is placed at table's perimeter
> and the antenna rotates around
> a circular path along table's perimeter.

Actually, "revolves" would be a better term for what you want to describe.

> Now you have the magnet stopped and a receiving antenna that is rotating.
> Does the antenna detect radiation from the magnet or not?

No.

> Is it the same situation, or not?

No.

> Notice that if the table doesn't exist and nothing else exists, except the
> magnet and the antenna, you cannot tell which of them is rotating and
> distinguish from both situations.

Wrong.

In the case of a rotating magnet, a centripetal force is required
to keep the outer part of the magnet rotating (provided by the
binding forces within the magnet). In the case of a revolving antenna,
a centripetal force is required to keep it revolving (provided by
whatever).

The two situations are thus clearly distinguishable.

> Which of them is radiating now? Is the magnet radiating? Is the antenna
> radiating? None of them radiates?

None.

[snip more of that]

> So, above I've prove that a stopped magnet also radiates.

No. You've only shown that you don't know how to transform between
rotating frames.

> Concluding I must say that your physics understanding is very poor.

ROTFL!

> A permanent magnet doesn't radiate.

If it rotates, it does.

Does a rotating permanent magnet have a time-dependent, oscillatory
magnetic dipole moment?

Is there radiation when there is a time-dependent, oscillatory
magnetic dipole moment?

If you answered "no" to any of these questios, please elaborate.

> All that you can say is that motion produces interaction.

He said nothing even remotely similar to what. It would be plain
nonsense.

> Since according to relativity theory there is no absolute rest frame of
> reference you can't ever say that a bar magnet is stopped.

Try to understand what relativity says about non-inertial frames.

You *do* know that a rotating frame is not inertial, don't you?

> Hence a bar magnet always radiates.

Wrong.

[snip]

> Relative motion is all that matters.

Wrong.

[snip]

Bye,
Bjoern

Relevant Pages

  • Re: Is electromagnetic field theory unified?
    ... can not prove that it radiates, ... > Again I say that I can prove that a stopped magnet also radiates. ... > Let us assume you place the antenna in short distance, ... You suffer from the disease the relativity wallahs call "frame ...
    (sci.physics)
  • Re: Is electromagnetic field theory unified?
    ... The fact is that I can prove you that a stopped magnet also radiates. ... Let us assume you place the antenna in short distance, ... Another suitable receiving device is a copper ring, ...
    (sci.physics)
  • Re: Is electromagnetic field theory unified?
    ... > that a spinning magnet radiates? ... (The only obvious exception is when a free electron radiates as a ... > No power transmitted, no interaction. ...
    (sci.physics)
  • Re: Is electromagnetic field theory unified?
    ... >> The reaction torque exerted by the radiated field on an antenna ... >> antenna, not magnet, since the reaction torque acting on an ... A rotating scatterer is a scatterer of EM radiation which is rotating, ...
    (sci.physics)
  • Re: Is electromagnetic field theory unified?
    ... >> antenna, not magnet, since the reaction torque acting on an antenna has ... Some object that scatters the incident radiation, ...
    (sci.physics)