Currents and symmetry

[quiet]

Case A: Ring with charge -2q turns and produces a magnetic field.
Case B: A ring with charge -q rotates in the same direction as the ring in the previous case. A parallel ring with charge + q rotates in the opposite direction.

Let's suppose that the rings are very thin and are very close together. Ideally we would say extremely thin and extremely close together.

The angular velocity has the same modulus in all the rings.

If I assume that the axes of rotation are all at rest relative to the observer and that Ampere's law is valid in both cases, then the magnetic field observed in case A and the magnetic field observed in case B are the same. Am I doing well here? I doubt because I am affirming the following.

For the observer who sees the three axes at rest, two systems that have different configurations produce the same effect.

I can not believe that the only effect of case B is to produce a magnetic (or electromagnetic) field equal to the field of case A. The difference in configuration should manifest itself in some effect. To say some effect is to say that I do not limit the possibilities to a magnetic or electromagnetic effect. An effect of another nature would also manifest the difference between both cases. Case B is perfectly symmetrical. Case A is asymmetric in comparison with case A.

Opinions, reasonings, hypotheses? Useful ideas to mathematically analyze something?

[Strange]

13 minutes ago, quiet said:

then the magnetic field observed in case A and the magnetic field observed in case B are the same. Am I doing well here? I doubt because I am affirming the following.

Surely, B results in two opposing fields that cancel one another?

But maybe I am confused by your references to charge instead of the more usual current. 

Oh, OK. I see you have reversed both charge and direction. And you are talking about a uniformly charged ring? Rather than a moving charge? So there will be no field in either case. 

17 minutes ago, quiet said:

Case B is perfectly symmetrical. Case A is asymmetric in comparison with case A.

They both seem equally symmetrical to me. 

[quiet]

11 minutes ago, Strange said:

Surely, ..

In case B, the net charge is equal to zero. That does not mean absence of charge. Rings with opposite sign charges, rotating in opposite directions, produce currents of the same direction and produce components of magnetic field that add up, to give in this case a net magnetic field equal to the field of case A. That is the idea. Well up there?

[Strange]

7 hours ago, quiet said:

In case B, the net charge is equal to zero. That does not mean absence of charge. Rings with opposite sign charges, rotating in opposite directions, produce currents of the same direction and produce components of magnetic field that add up, to give in this case a net magnetic field equal to the field of case A. That is the idea. Well up there?

In A, do you have a single charge going in circles, or a uniformly charged ring that rotates?

[studiot]

You need to put a diameter/radius to these rings.

Atom sized?

1mm?

Then you can discuss what makes the charge(s) circulate as you describe.

One positive and one negative?

Positron and electron or what?

Antimatter/matter?
Very close together?

 

There are lots of hypothetical situations where simple theory quickly runs into difficulty.
Especially vague ill specified ones.

 

As regards the circulation (and your other thread) read this about Maxwell's original ether.

 

[swansont]

13 hours ago, quiet said:

For the observer who sees the three axes at rest, two systems that have different configurations produce the same effect.

I can not believe that the only effect of case B is to produce a magnetic (or electromagnetic) field equal to the field of case A. The difference in configuration should manifest itself in some effect. To say some effect is to say that I do not limit the possibilities to a magnetic or electromagnetic effect. An effect of another nature would also manifest the difference between both cases. Case B is perfectly symmetrical. Case A is asymmetric in comparison with case A.

Opinions, reasonings, hypotheses? Useful ideas to mathematically analyze something?

They don't produce the same effect. Case A produces an electric field at some distance away, while case B does not.

[Strange]

1 hour ago, swansont said:

They don't produce the same effect. Case A produces an electric field at some distance away, while case B does not.

Am I right in thinking that if the ring (case A) is uniformly charged, there will be no magnetic field created? Or is it equivalent to a current flowing through the ring?

edit: On second thoughts I assume the latter; as spinning charged particle generates a magnetic moment

Edited December 14, 2018 by Strange

[quiet]

@strange
Uniform charge density in all rings.

@swansont
Its true. It is not the same total effect. Can be the same magnetic field in both cases?

[Strange]

45 minutes ago, quiet said:

Can be the same magnetic field in both cases?

Having now convinced myself that there is (or could be) a magnetic field, I don't see why there shouldn't be a difference between the presence of an electric field and a magnetic field in the two cases.

What you suggest looks a bit like the technique of minimising the magnetic field (or EM radiation) from signal wires by, for example, using a twisted pair (so the fields generated by the outward and return currents cancel out). Or, the opposite of that, perhaps...

 

[swansont]

50 minutes ago, quiet said:

 
@swansont
Its true. It is not the same total effect. Can be the same magnetic field in both cases?

As far as I can tell, yes.

 

[quiet]

@strange

@swansont

Very clear and helpful your answers. Thanks!

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Are we all admitting that an electrically neutral system can have an effective magnetic field?

Of course, magnetic stones are neutral systems and have effective magnetic field. Anyway, the atomic and molecular configuration of a stone differs quite respect two rings. Or not?

Edited December 14, 2018 by quiet

[swansont]

1 hour ago, quiet said:

@strange

@swansont

Very clear and helpful your answers. Thanks!

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Are we all admitting that an electrically neutral system can have an effective magnetic field?

Indeed. A chunk of any ferromagnetic material can have a strong field and be electrically neutral.  A current-carrying conductor typically has a magnetic field (unless you go to lengths to mitigate it) but has no net charge.

1 hour ago, quiet said:

Of course, magnetic stones are neutral systems and have effective magnetic field. Anyway, the atomic and molecular configuration of a stone differs quite respect two rings. Or not?

One could think of a hydrogen atom as an analog (though there are limits to any analogy that crosses between the QM and classical divide). While we know electrons and protons are not physically spinning, they do have magnetic moments, and you can align the spin axes either up or down. And you can have the electron in a state where it has orbital angular momentum. So you can have a system where charges cancel but you have a magnetic field. (see also: neutrons) You can have a system that is charged, and has a magnetic field, or has no magnetic field.

https://en.wikipedia.org/wiki/Magnetic_moment#Atoms,_molecules,_and_elementary_particles 

[studiot]

2 minutes ago, swansont said:

One could think of a hydrogen atom as an analog (though there are limits to any analogy that crosses between the QM and classical divide). While we know electrons and protons are not physically spinning, they do have magnetic moments, and you can align the spin axes either up or down. And you can have the electron in a state where it has orbital angular momentum. So you can have a system where charges cancel but you have a magnetic field. (see also: neutrons) You can have a system that is charged, and has a magnetic field, or has no magnetic field.

Which was why I asked about size earlier on.

 

Quiet please indicate the size of the systems you are contemplating, along with the eventual direction/destination of your enquiry.

 

Have I mentioned Rowland's ring theory in relation to magentism before?

[quiet]

@studiot

I am thinking about a classical case, whose diameter can be, for example, 2.5 m. I choose this diameter because I want introduce later the case of two cylinders, wich differ a bit in diameter, have the same rotation axis (one cylinder placed into the other, like a cylindrical capacitor).

Between both cylinders there are a radial electric field and an axial magnetic field. These fields are mutually perpendicular. Then, the Poynting vector that both form is tangent to the circumferece (sorry if language errors). There is a movement of EM energy around the circumference.

Can this movement of EM energy remain in uniform angular distribution? Or a wave is formed between both cylinders?

The region between cylinders have a contour, not equal to a waveguide, but able to reflect elemental waves and stablish waves groups. Waves groups naturally exhibit quantization. I do'nt know all details implied in this case.

Edited December 14, 2018 by quiet

[studiot]

20 hours ago, quiet said:

Case A: Ring with charge -2q turns and produces a magnetic field.
Case B: A ring with charge -q rotates in the same direction as the ring in the previous case. A parallel ring with charge + q rotates in the opposite direction.

So we have a ring of conductive material eg a hoop of wire?

This ring is charged to a value of -2q, where q is much larger than the charge on one electron. So it is not electrically neutral  then disconnected from the source of charge but insulated from the rest of the universe?

The ring is then rotated with some (steady ?) velocity v ?

Why should this scenario result in a magnetic field?

 

Are you trying to experiment with homopolar motors and generators AKA a Faraday Disk?

Edited December 14, 2018 by studiot

[quiet]

@studiot

So we have a ring of conductive material eg a hoop of wire? Yes.

This ring is charged to a value of -2q, where q is much larger than the charge on one electron. So it is not electrically neutral  then disconnected from the source of charge but insulated from the rest of the universe? Yes.

The ring is then rotated with some (steady ?) velocity v ? Yes.

Why should this scenario result in a magnetic field?  A ring that has an electric charge and rotates is equivalent to a current loop.

Are you trying to experiment with homopolar motors and generators AKA a Faraday Disk? It is not my intention. In case of similarity, I have not looked for that.

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I have not been able to edit a previous post to add a data. So in this post I copy the content again and add what was missing.

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I am thinking about a classical case, whose diameter can be, for example, 2.5 m. I choose this diameter because I want introduce later the case of two cylinders, wich differ a bit in diameter, have the same rotation axis (one cylinder placed into the other, like a cylindrical capacitor).

The inner cylinder is in rest respect to the observer.

Between both cylinders there are a radial electric field and an axial magnetic field. These fields are mutually perpendicular. Then, the Poynting vector that both form is tangent to the circumferece (sorry if language errors). There is a movement of EM energy around the circumference.

Can this movement of EM energy remain in uniform angular distribution? Or a wave is formed between both cylinders?

The region between cylinders have a contour, not equal to a waveguide, but able to reflect elemental waves and stablish waves groups. Waves groups naturally exhibit quantization. I do'nt know all details implied in this case.

Edited December 14, 2018 by quiet