Do Magnetic Fields Do Nonzero Work on Moving Objects?

[sweet springs]

Born2bwire, Thanks for your quick and detailed answer. also to you, sophiecentaur.
Let me confirm my understanding of what you say.

Since these currents are from the atomic orbitals, there is no need to keep supplying energy because the orbitals are stable themselves. On a very basic level, if we have an electron orbiting in a circle, we do not need to expend any energy to keep it orbiting, only a constant force. However, when we ourselves physically move the magnets around a magnetic field, we are inputting and taking out energy from these orbitals. That is, if I pull two magnets apart, I impart work that gets injected back into the magnetic fields. This would correspond to adding energy into the electron orbits.

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Do the two types of the equivalent large loop currents, i.e.
A adding up of atomic loop currents of a magnet
B net loop current in a superconducting ( or zero resistance ) circuit
behave differently under a magnetic field, i.e.
A keep accelerated
B stop accelerated after all the current kinetic energy are transferred to the whole body kinetic energy
?
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Regards.

 

[sweet springs]

Hi. No reply means agreement, I guess and go on.

【Question】At t=0 in no gravitational vacuum space, The same type of two magnets are placed still counter.
Figure 　　０------｜------０
One of the magnets should be replaced by one of the followings of the same shape and the mass.
A-1 A closed loop net current, equivalent to adding up of atomic loop current, in the wire of resistance R.
A-2 A closed loop net current, equivalent to adding up of atomic loop current, in the wire of resistance 0.
B-1 A loop net current, equivalent to adding up of atomic loop current, conditioned constant during the process by the designed electric circuit and battery inside the body, in the wire of resistance R.
B-2 A loop net current, equivalent to adding up of atomic loop current, conditioned constant during the process by the designed electric circuit and battery inside the body, in the wire of resistance 0.
C Arranged molecules composed of S monopole, the distance bar and N monopole, equivalent to adding up of atomic loop current

Q1. Which ones move the same way as the magnet?
Q2. As for them where do kinetic energy come from?

【Answer】
A1. B-1,B-2 and C. B-1 generates heat Q also.
A2. The kinetic energy of the body is
Magnet: -∫ｄVmagnet　M・ΔH　 where ΔH =（▽H・v + ∂H/∂t）Δt , change of magnetic intensity.
B-1: -Δ(energy in battery)
B-2: -Δ(energy in battery) - Q
C : -Δ（stress energy stored in the bar)　　　

Does this QA make sense?
My remaining interest in this issue is, How M・ΔH≠0 and q(vXB)・v=0 harmonize?

Magnetic fields do NOT work on particles with 0 spin, but DO work on particles with charge and spin, don't they ?

Regards.

 

[cesiumfrog]

ah, magnetic fields, the invisible inclined slopes..

The magnets are pinched still. there's no electric field. Then at time zero they are released and start to move. In such a case, zero electric field at time zero could be the driving force?

(Haven't read the whole thread but) I see your point that some initial work appears to be done by a field that is purely magnetic. The fact is that the rule "magnetic fields do no work" was never really intended to apply to intrinsic magnetic dipoles (just as it would not apply to free magnetic monopoles). Nonetheless, in the case of the atoms of your magnet, even the intrinsic magnetic dipole can to a reasonable extent be attributed to rotation in the electron cloud/orbital (and could be modeled like a tiny electric current loop with zero resistance), and from the rest frame of any point in this rotating charge distribution (unlike the rest frame of the whole atom or apparatus) there actually is an external electric field (due to relativistic effects which naturally explain magnetic force) acting even at time zero.

 

[kcdodd]

You have to make a distinction between a magnetic dipole formed by "spinning electric charge", and that which would be formed by two magnetic charges (a pure dipole). Spinning charge has some internal energy associated with the rotation, and so any work done comes from this and not the magnetic field. I do not know for sure which type quantum spin is.

 

[sweet springs]

Dear kcdodd. Thanks for your comment.

Let me classify circulation of current in the following three.
A net current in artificail loop circuit
B quantum motion of electrons around the core in atom
C quantum spin of charged particle

On case A, I agree you

Spinning charge has some internal energy associated with the rotation, and so any work done comes from this and not the magnetic field.

But as for quantum cases B and C, I am not sure if such motions can tenure energy in the system and sometimes pour it our for kinetic enrgy increase. Regards.