Re: Is electromagnetic field theory unified?

From: Bjoern Feuerbacher (feuerbac_at_thphys.uni-heidelberg.de)
Date: 02/25/05 

Date: Fri, 25 Feb 2005 13:28:05 +0100

JM Albuquerque wrote:
> "Gregory L. Hansen" <glhansen@steel.ucs.indiana.edu> escreveu na mensagem
> news:cvkrku$hci$1@rainier.uits.indiana.edu...
>

[snip]

>>It takes [nobody cares what's on the inside] to create the field.
>
>
> I do care a lot about what's inside.

That suggests that you are only familiar with Maxwell's equations
in their integral form.

[snip]

>>Any
>>number of magnets and coils moving in arbitrary ways, it doesn't matter.
>>Maxwell's equations are differential equations-- the field at a point
>>depends on the fields immediately surrounding it. There's only an
>>indirect dependence on the sources, in that the sources create some
>>fields. But as long as the fields around the point of interest are the
>>same it doesn't matter where they came from.
>
>
>
> The point is that you have no unitary sources of magnetism.
> There are no magnetic monopoles.

Indeed.

> That makes all the difference between electric and magnetic.

If we compare the behaviour of electric dipoles with the behaviour
of magnetic dipoles, it's totally irrelevant that no magnetic
monopoles exist.

> The magnetic field is always "closed".

Indeed. So what?

> The electric field could be open if there is only one kind of charges
> present and it will close if equal amount of the other kind of charges is
> inside the integration volume.

Wrong. Some of the lines will close, but a lot will still be open.
Look up "electric dipole field".

[snip]

>>Spin that magnet for one minute, and then stop it. Place the observer two
>>light-minutes away. What kind of field will he see, and what is the field
>>doing in the minute between stopping the magnet and arriving at the
>>observer?
>
>
> It depends on the receiver.

No, the field that is seen does *not* depend on the receiver.

Where do Maxwell's equations mention the receiver, in your opinion?

> The receiver must be an inductance.
> Since you've introduced the time coordinate one must talk about power.
> (power = energy/time)

No, we don't have to. Not every time someone mentions time, one has
to talk about power!

> It depends on the power factor (cosine of phi).

No, it doesn't. There is no power factor for electromagnetic radiation
in a vacuum.

> No power transmitted, no interaction.
> If power is absorbed, there will be interaction and radiation will build
> around the receiver (current in phase with voltage will flow).
>
> The electric field could have voltage and current be in phase or
> lagging 90 degrees depending if power is transmitted or not.
>
> The general equation for the instant power P(t) is from text book's:
> P(t) = VI cos(phi) - VI cos(2wt - phi)
> phi = Arctan (wL/R)
>
> Work around these formulas and you will see that if cos(phi)=0
> (power factor zero) power oscillates between the source and the
> receiver at double frequency and no energy is lost, nor any power
> transmitted.
>
> The receiver does all the difference.

All of these formulas are right for AC circuits, and have exactly
nothing to do with electromagnetic radiation.

[snip]

>>>Experience with coils and magnets.
>>>You cannot creat current with a static magnetic field but you can creat
>>>a magnet with DC current.
>>
>>And what is the wave equation outside of a region that contains sources?
>
>
> Static sources?

No matter what sources.

> With static sources you got no wave, no radiation.
> If the sources move the wave will depend on that.

He asked what the *wave equation* looks like, not what the waves
look like.

Are you too stupid to understand the question, or are you deliberately
obtuse?

Bye,
Bjoern

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