Can a magnet's magnetic field perform work on another magnet?

[Dale]

My post above refers to definitions,accepted nomenclatures.What word(s) would you use to name the force on the paperclip or the current carrying wire?The "magnetic" force seems to be a preferred description according to searches I have made so far.See,for example,the MIT lectures on the subject.
If we were not to call it the magnetic force then I have suggested that the electromagnetic force may be a better description,but is this being too fussy?.I imagine that most textbooks(at least up to A level standard)would still continue to refer to the "magnetic" force so as to distinguish it from the electric force between stationary charges.

Force is different from work. I would call it a magnetic force or a Lorentz force. But the magnetic part of the Lorentz force does no work, at least not directly.

 

[Dale]

I'm not touching the can in any way. It moves only electrostatically. It's a textbook example of an electric field, Dale.

The balloon is charged and has an E field, but since the can is a conductor it won't exert a net force on it. At least, I think not. Do you have a reference?

To Q-reeus, see, I do ask other people to provide references, not just you.

 

[Dale]

And vice versa any work done by E and j is only through its impact on B.Chicken and egg or a comprimise by calling it electromagnetic?

No, not vice versa, but the compromise wording is fine.

 

[Dotini]

The balloon is charged and has an E field, but since the can is a conductor it won't exert a net force on it. At least, I think not. Do you have a reference?

When an uncharged object is placed near a charged object its charges rearrange themselves. Those charges attracted to the charged object move towards the charged object and those charges repelled move away. This effect is known as polarization.

Since the balloon is negatively charged and the Coke can is acting as if it is positively charged, the Coke can is attracted to the balloon. The force of attraction is so strong, in fact, that the Coke can begins to roll towards the balloon!
http://phun.physics.virginia.edu/demos/electrostatics.html

Respectfully submitted,
Steve

 

[Dale]

http://phun.physics.virginia.edu/demos/electrostatics.html

Cool reference, thanks. I will go back and re answer the earlier post you made now that I understand what you were saying.

 

[Dale]

I can create a charged object by rubbing a balloon on my hair. And then do work with it by rolling an aluminum can around on the floor. No magnet is required in this instance, as the work is done by an electric field.

Is this agreeable?

Yes, the work is done by the E field, given by E.j as usual.

 

[Q-reeus]

Tell me how I am twisting this out of shape:
Originally Posted by Q-reeus: "So a long straight magnetized rod enclosed within a similarly shaped solenoid should completely demagnetize when the solenoid generates a B field Bs equal in magnitude and of the same sign as that of the magnet's initial B field Bm. ... This manifestly does not happen."

For the same manifestly obvious reasons as before - you take it out of context and proceed to give it an erroneous slant. You failed to quote both the preceding and following portions of my entry there. Do that, and the claim I am trying to 'overthrowing Maxwell's eqn's' is seen as distortion at best. Anyway, how about you explaining the stability of atoms using just Maxwell's eqn's - or are you indeed ignorant of the classical prediction that electron's must in-spiral to the nucleus in a very brief time? ME's really do have their limitations.

 

[Q-reeus]

Q-reeus: "Electrical interactions of the E.j type simply do not and cannot apply in that wholly QM regime."
I agree.

But do you really? Then what of this from #18 (a quote from your own earlier posting):

Q-reeus: "I just managed to find the following, which might give pause for thought: http://physics.stackexchange.com/que...agnetic-dipole" [Broken]
The derivation there is for force density, not power density. If you go through the next step then you get E.j. As I said in in my point 4 both E and j depend on B, so it does work indirectly.

That link to elsewhere was all about magnetic interaction with a fundamental magnetic dipole - i.e. electron's magnetic moment. You there claimed it still was explainable in terms of E.j energy interactions 'in the final step'. But now you agree with me? I'm confused - over where you really stand on this. Please clarify.

Q-reeus: "And it carries over to a permanent magnet as a QM glued ensemble of such."
I do not agree. If this were correct then classical mechanics would never be valid as every classical object is a "QM glued ensemble". As long as the energies and masses in your system are all much larger than the Planck scale then you are in the classical limit of QM and classical physics applies.

More nonsense. Have you not noticed my reference in #10 to the supercurrent situation? You do believe in the existence of quite macroscopic superconductivity (let's not forget superfluidity and one or two other more delicate phenomena like BE condensates)?

Q-reeus: "I notice you still haven't supplied any kind of coherent rebuttal to either #5 or #10."
Correct, and I will not until you provide some solid supporting evidence. The burden of proof is on you, not me; I will not accept it simply because you cannot be bothered to support your own claims. I have supported mine.

You only claim to. Actually, having taken a long time to make your public declaration of a 'final decision' here: https://www.physicsforums.com/showpost.php?p=4024036&postcount=348, it is only to be expected you now find it so hard to face up to having made a wrong decision. And btw, having accused me of 'wanting to overthrow established mainstream science' back in your #9, I find it a particularly ironic statement given, as my trawling backwards through that earlier thread has found, this choice opening position of yours there: https://www.physicsforums.com/showpost.php?p=4005572&postcount=54. Having yourself adopted my current 'heretical' position (for the wrong reasons though) right up to that later posting linked above, one might have expected a little more understanding - you know, a "Hey, I can understand that view - it had been mine life-long right up till a short while ago!" Nothing of the kind. So, evidently you believe in a life principle of being especially kind, gentle, and understanding toward yourself, but it's ok to put the boot into one's opposition via regular misquotes and innuendo. All's fair in love (or hate) and war seems your abiding motto DaleSpam.

 

[Q-reeus]

Classically, permanent dipoles are modeled as the limiting case of a current loop shrinking to zero size, but in a way that leaves its magnetic dipole moment constant.

That can be done sure, but it's not the whole story.

As you point out, this model is not entirely accurate ( for one there must somehow be some mysterious energy source which keeps the magnetic dipole moment constant when subjected to external field, not to mention that elementary particles like electrons have a dipole moment associated with them that only comes in quantized values), but it does correctly predict the net force and torque on permanent dipoles without introducing an additional axiom to theory (one treating magnetic dipoles as fundamental and different from the other two types of fundamental sources, point charges and currents).

I respectfully disagree. There *must* be a fundamental break from classical behavior just in order that those 'point dipoles' have unchanging magnitudes during magnetic interactions. It is the central point of my #5 and #10.

 

[Q-reeus]

Dotini, there is no contradiction between the quote you give and the fact that magnetic fields don't do work. Of course, if you compare the final state (paper clip attached to the magnet) with the initial state (paper clip separated from the magnet), you of course find that the change in magnetic-field energy is given by the work necessary to pick up the paper clip, attaching it to magnet.
This is precisely the content of Poynting's theorem, nicely explained at DaleSpam's link. This epxlains the the work is done by induced currents and electric fields during the transient (i.e., time-dependent!) situation when picking up the paper clip!

Missed responding to this before but address now - given your weight here as currently the thread's only expert/authority figure. If your claim that -dA/dt E fields acting on induced currents explains the above, I invite you, as someone familiar with both classical and QM regimes to apply that to what I brought up in #10. Do you disagree with my observation there that flux quantization in wholly superconducting circuits directly implies the failure of dW = E.j dv over an interval of magnetic interaction where supercurrent I_s is forced constant, despite a changed increment of enclosed flux and thus a changed A.I_s dl, where dl is an incremental length along the thin supercurrent? This despite that *on average* that quantity is invariant in a superconducting circuit - i.e. *on average* enclosed flux is an invariant? Moreover that as the superconducting circuit is shrunk smaller, so the interval of applied external B field variation over which I_s = constant grows in inverse proportion to enclosed area? Do you further agree or not with my observation that an electron is in a sense the ultimate endpoint of shrinking, not a classical, but a superconducting, loop current re it's magnetic interactions? And that in that case there are precisely zero conditions in which E.j is relevant to electron-as-magnetic-dipole? And that a permanent magnet is an ensemble of such fundamental dipoles - notwithstanding that *quantized* electron orbital motion contributes to magnetization here, though generally to a minor degree? (Earlier I had specified fully magnetized when referring to interactions involving permanent magnets owing to it simplifying things, but that restriction can be dropped with no consequences for the argument here.) And that induced eddy currents - which may be treated as behaving entirely classically, are in general a very minor consideration - especially for slow relative motions and for certain materials such as 'hard' ferrites? I shall be interested to see how or whether you choose to deal with hopefully all of the above questions.

 

[Dale]

For the same manifestly obvious reasons as before - you take it out of context and proceed to give it an erroneous slant. You failed to quote both the preceding and following portions of my entry there. Do that, and the claim I am trying to 'overthrowing Maxwell's eqn's' is seen as distortion at best.

So do you or do you not assert that Maxwell's equations predicts the complete demagnetization of any magnet due to an equal applied field? And do you or do you not believe that prediction is contrary to observation?

Just because I quote only a portion of your post does not mean that I am misrepresenting your position.

 

[Q-reeus]

So do you or do you not assert that Maxwell's equations predicts the complete demagnetization of any magnet due to an equal applied field?

Not any magnet - a hypothetical 'magnet' comprised of classical perfectly conducting loop currents. And honestly, this was manifestly and clearly evident in my #5 - why do you keep asking the same questions to obvious answers?

And do you or do you not believe that prediction is contrary to observation?

I refer you back to #5!

Just because I quote only a portion of your post does not mean that I am misrepresenting your position.

Be honest DaleSpam - this has become a deeply personal thing, spanning a considerable time now over many past threads. You resent my style of 'irreverent' balloon pricking - especially when that balloon(s) are your's.

 

[Dale]

More nonsense. Have you not noticed my reference in #10 to the supercurrent situation? You do believe in the existence of quite macroscopic superconductivity (let's not forget superfluidity and one or two other more delicate phenomena like BE condensates)?

In superfluidity, BE condensates, and superconductivity the thermal energy is small compared to the Planck scale. My comment applies to all of them as well.

You only claim to. Actually, having taken a long time to make your public declaration of a 'final decision' here: https://www.physicsforums.com/showpost.php?p=4024036&postcount=348, it is only to be expected you now find it so hard to face up to having made a wrong decision.

The difference between that conversation and this being that vanhees71 actually presented me with good evidence supporting his point, in the form of solid references and good derivations from accepted theory.

That is something you have never done in any of our conversations. Should you ever decide to do likewise then you stand a good chance of changing my mind, but as it is your positions consistently appear to me to be both impervious to and unsupported by any good evidence.

Post some good evidence and then I will resume the discussion with you here, otherwise we are just wasting time and adding unnecessary tension to the forum.

 

[Q-reeus]

In superfluidity, BE condensates, and superconductivity the thermal energy is small compared to the Planck scale. My comment applies to all of them as well.

You have shifted ground unannounced, but not enough to salvage that bit: Here's the original passage above bit originally referred to:

Q-reeus: "And it carries over to a permanent magnet as a QM glued ensemble of such."
I do not agree. If this were correct then classical mechanics would never be valid as every classical object is a "QM glued ensemble". As long as the energies and masses in your system are all much larger than the Planck scale then you are in the classical limit of QM and classical physics applies.

A blanket statement - and confused at that. Why do you choose the Planck scale as demarcation point - for both energies and length? It's crazy and excludes everything above fundamental particle if even there. Atoms for instance would far from qualify as a fundamentally quantum object.

Q-reeus: "You only claim to. Actually, having taken a long time to make your public declaration of a 'final decision' here: https://www.physicsforums.com/showpost.ph...&postcount=348 [Broken], it is only to be expected you now find it so hard to face up to having made a wrong decision."

The difference between that conversation and this being that vanhees71 actually presented me with good evidence supporting his point, in the form of solid references and good derivations from accepted theory.

I can accept and respect that you believe that position, but...then:

That is something you have never done in any of our conversations.

You mean 'not something I accept'. The essence of my position is well enough put - and evidently Lubos Motl is similarly dismissed as 'crackpot'.

Should you ever decide to do likewise then you stand a good chance of changing my mind, but as it is your positions consistently appear to me to be both impervious to and unsupported by any evidence.

Evidence? It is fundamentally a conceptual issue one either 'gets' or not.

Post some good evidence and then I will resume the discussion with you here, otherwise we are just wasting time and adding unnecessary tension to the forum.

If you don't want unnecessary tension then avoid making blanket accusations and distorting my words - you well know I don't take that lying down. And how about you actually dealing with certain questions I posed earlier - answering them may help you.
From #42:

Anyway, how about you explaining the stability of atoms using just Maxwell's eqn's - or are you indeed ignorant of the classical prediction that electron's must in-spiral to the nucleus in a very brief time? ME's really do have their limitations.

And you know the context to that one - so don't twist it to suit.
Finally, kindly this round, actually do answer my question in the earlier part of #43 - will you now clarify what seems to be a contradictory position?

 

[Miyz]

I'm lost with all this... Please if someone can simply present an answer.
Yes/No, supporting a simple explanation?
I've lost myself with all this confusion.However, noticed that Van & Dale are still referring the same answer used in my previous thread.

Interesting.





Miyz.

 

[Dotini]

You can pick up a paper clip with a magnet. You can pick up another magnet with a magnet. That much is clear. Beyond that, authorities differ.

Respectfully,
Steve

 

[harrylin]

Shocking and disconcerting that physicists and perhaps even textbooks are in disagreement! [..]

As we discovered in the original thread, it's basically a matter of words. Some people use a (IMHO strange) definition of "work", such that the use of field energy for displacing an object is not "work" done by that field.

I guess that if I pull on an object with a rope and ask if I "did work", some may answer yes, others may answer "no, the rope did the work" and again others may answer that depending on the system boundaries that we regard, if it was me or the rope that did the work. I would say that I performed work on the object by means of the rope.

I'm lost with all this... Please if someone can simply present an answer.
Yes/No, supporting a simple explanation?

See above; so I simply say Yes, in agreement with Robert Gardner. :tongue2:

My more complete answer (based on the elaborate explanations of others):
Yes, the magnetic field does work by means of induced currents and electric fields.

However it's unclear to me where/how such currents occur in permanent magnets. Does this mean that they heat up? If this was explained somewhere, can someone please provide a link?

 

[Q-reeus]

See above; so I simply say Yes, in agreement with Robert Gardner.

Good for you Harald - but then you muddy the waters with:

My more complete answer (based on the elaborate explanations of others):
Yes, the magnetic field does work by means of induced currents and electric fields.

What induced currents? [it's true there are c(∇×M) 'induced currents' in the case of that soft iron paper clip, where induced magnetization is significant. Fundamentally though, such 'currents' owing to changing orientation of fundamental spin moments are fictitious entities. In the case of fully magnetized permanent magnets, there is no room to invoke such at all] Have you read through my little piece addressed to vanhees71 in #45? And btw this can be extended not just to permanent magnets but anywhere that magnetic media are involved - e.g. transformers, and real motors incorporating 'soft' iron armatures etc. We are talking about how energy is redistributed in an interacting system, so 'work being done' is as you say perhaps a little ambiguous. What can be said is there is for sure no electrical E.j work being done on those fundamental magnetic entities - electron as magnetic moment. The only consistent classical way of treating them is as perfectly rigid (sans SR length contraction) fictional magnetic dipoles with magnetic charges at each end. That's in terms of their impact on the *externally accessible* system energetics - magnetic susceptibility of the media. There is a somewhat 'delicate' issue raised in my #7 if one follows it through ('excess internal energy'), but it's really a matter for a separate thread that I may later open probably in QM section not here.

 

[harrylin]

Good for you Harald - but then you muddy the waters with:
[...]
What induced currents? [..]

Good - so now we are two who are asking that same question! :tongue2:

I did not study your exchange which appears to somewhat challenge "standard science", instead I wait with interest on more explanation by those who make such claims.

 

[Miyz]

Then the conclusion of this thread is that magnet's can do work on each other.
But what force exactly is the cause of work?

 

[Miyz]

Anyone?!

 

[Dale]

You are not going to get a consensus conclusion on this thread. My conclusion is the same as the previous thread since this is still a situation covered by the laws of classical EM. Others have firm differing opinions but no good evidence to support them.

You should form your own opinion either based on evidence and the laws of physics or based on unsubstantiated speculation, as you prefer.

 

[cabraham]

You are not going to get a consensus conclusion on this thread. My conclusion is the same as the previous thread since this is still a situation covered by the laws of classical EM. Others have firm differing opinions but no good evidence to support them.

You should form your own opinion either based on evidence and the laws of physics or based on unsubstantiated speculation, as you prefer.

So what's your conclusion? What is the basis? I just would like to know.

Claude

 

[Miyz]

So what's your conclusion? What is the basis? I just would like to know.

Claude

His first post is the main conclusion. It's the same as the preview thread that I've started, unfortunately Dale and I disagree. I honestly do not believe that the same concept on a "loop" is applied to a "permanent magnet".

Miyz,

 

[Miyz]

However, we could make this conclusion more debatable. Maybe?

 

[Q-reeus]

I can only repeat what has been put already. It is an experimental fact that ferromagnetic and ferrimagnetic media do not respond to an induced magnetic field as though composed of microscopic perfectly conducting classical loop currents. If it were so then net magnetic induction B_tot within such media would attempt to be invariant, in keeping with the requirement that no electrical field exist within, or have a tangent component at the surface of, such conducting entities - only satisfied if the net flux enclosed within each such loop current is maintained constant (perfect diamagnetism - see e.g. www.phy.duke.edu/~hx3/physics/Superconductor2.pdf [Broken]). And that predicts a net media susceptibility -> - 1. [Magnitude would be somewhat less than unity owing to thermal jostling, and less than 100% achievable volume packing fraction of such loops] Does not happen that way. Actual susceptibilities can run into the hundreds of thousands for magnetically 'soft' media, while essentially zero for permanent magnets in their useful range of use. Quantum mechanics rules here and what is invariant is not enclosed flux within such hypothetical loop currents, but rather the magnitude of the intrinsic electron dipole moment.

To claim E.j work is being done on such intrinsic moments is inviting a severe paradox since, as touched on in #26 "there must somehow be some mysterious energy source which keeps the magnetic dipole moment constant when subjected to external field," (actually, time-changing B field giving rise to non-zero E.j) There is indeed something to this 'mysterious energy source' which bears further thought as per my closing bit in #53. At any rate, actually observed magnetic response, whether of permanent magnets or transformer cores etc., is best thought of in terms of fictitious magnetic dipoles of fixed magnitude - and that property cannot be explained via tiny classically behaving loop currents. And if one cannot then model using such loop currents, the whole argument that all energy exchanges are explained as E.j interactions simply fails.

For real situations there is finite conductivity and it's this generally quite minor induced eddy-current component that can be explained without controversy as E.j interactions. In the case of induced magnetization (e.g. example of soft iron paper-clip attracted to permanent magnet), there is a formal 'induced current' interaction but only in the sense of a varying magnetic moment m in F = ∇(m.B), the interaction being consistently best treated as fundamentally magnetic not electric.

 

[Miyz]

You are not going to get a consensus conclusion on this thread. My conclusion is the same as the previous thread since this is still a situation covered by the laws of classical EM. Others have firm differing opinions but no good evidence to support them.

You should form your own opinion either based on evidence and the laws of physics or based on unsubstantiated speculation, as you prefer.

What evidence's do you need? Dale, the basics of all of this is that magnet's certainly can do work. What exactly is doing the work? I find that difficult to prove. However, a known FACT is spread around the field of EM is that magnet certainly can do work. Example: Take them apart and put them back to each other. Now we can debate all night on who is exactly is doing the work but again, magnets can certain do work they have the force,potential to do so. I told you from before that when asked what work is... You would reply that it's the transfer of energy. Ok, fair enough. But for ANY SYSTEM in the universe that transfer's energy there has to be a source of force or multiple force's that would lead to that conclusion eventually. So we need to break it down and find what force/forces that is.


I agreed earlier that magnetic fields/forces do work but INDIRECTLY to a loop of wire. However, in case of a magnet things would totally differ here. When a magnet is placed in a non-uniform magnetic field it certain feel's a force that "force" can do work on that magnet. What generates a non-uniform magnetic field well, that can be another manget or another electromagnet...

Best Regards,
Miyz,

 

[Miyz]

Ok, the electrical forces are the cause of work. Agreed. However! Who's the main cause of the electrical forces? This is the main question I feel is left ignored and I would say that its the magnetic fields/forces and their interaction that would eventually cause the electrical forces to do work. Without one of those factors. As I said earlier before magnetic fields would generate those electrical force that would eventually cause the work. Without one of them NO WORK would be done on a system.

Electric forces CAN NOT! be generated in this system without the existence of a magnetic field/force. The greater/weaker the field the same goes for the EF. So Mag.F + Elec.F are both proportional to each other.

Does this sound good everyone?(Correct me if I'm wrong/or not liking where this is going)

Miyz,

 

[Q-reeus]

Ok, the electrical forces are the cause of work. Agreed.

Not agreed. You sure seemed to be disagreeing with that position in #62 - what has changed your mind? Apparently my summarized position in #61 has not impressed , or is it a case of not quite getting the main point there?

 

[Miyz]

Not agreed. You sure seemed to be disagreeing with that position in #62 - what has changed your mind? Apparently my summarized position in #61 has not impressed , or is it a case of not quite getting the main point there?

Im still not sure with my final conclusion. More confused then ever! However, my post #62 makes the most sense to me personally. I find you're post was great! Perfectly well demonstrated but I asked so many all agree that electrical forces are doing the work not magnetic. I don't how to rebuttal to that point honestly because I feel this fact is still not proven properly. However, if you have something please share more.

 

[Q-reeus]

Im still not sure with my final conclusion. More confused then ever! However, my post #62 makes the most sense to me personally. I find you're post was great! Perfectly well demonstrated but I asked so many all agree that electrical forces are doing the work not magnetic. I don't how to rebuttal to that point honestly because I feel this fact is still not proven properly. However, if you have something please share more.

Yes I agree it can get confusing, but it's good to keep in mind the main issue in this thread. We are debating the means whereby *energy* is exchanged/redistributed amongst interacting magnetized structures - say that paper-clip/magnet, or magnet/magnet. These are ferromagnetic (iron & similar compounds) or ferrimagnetic (ferrites) materials whose magnetism is not owing to currents flowing through wires, but chiefly the intrinsic magnetic moment of electrons - with electron orbital contributions significant in ferrites. As covered in say #45 and #61, it is known the electron intrinsic magnetic moment, and to only a slightly lesser degree ferrimagnetic orbital contributions, simply does not 'feel' any electrical forces of the -dA/dt type (result of relative motion or internal reorienting of magnetic material). If it did there would necessarily be a change in the intrinsic magnetic moment as per #61 - and it just does not happen. It's a bit like there being a spinning top on the table. A classical spinning top (the usual ones!) will immediately slow down if one presses down on it with the hands, but an intrinsic quantum top would magically resist all such efforts - as though it just becomes perfectly frictionless. I hope you get the analogy. [STRIKE]Flux[/STRIKE] Spin/magnetic moment quantization forces real magnets to completely ignore electrical fields that would readily induce changed magnitude of magnetic moment in a classical microscopic loop current. [Edit: only wholly true of intrinsic spin magnetic component. Orbital part is more complex and somewhat 'softer' in that orbitals do deform slightly under an applied external B, allowing a small but finite continual response in net magnetic moment. The complete description of all contributions to magnetic response and origins is complex - e.g. "www.appi.keio.ac.jp/Itoh_group/spintech6/lectures/Lec1_Weiss.pdf" [Broken] Net response very different though to the diamagnetism predicted for E.j action on a classical perfectly conducting loop current]

There continues to be forces felt, but the distribution of such forces and resulting energy redistribution - work done by one part of the system on another, is drastically different between the case of real magnetic materials that reject E.j interactions, and hypothetical media comprised of classical loop currents that would not. The former behave as though rigid dipoles made of magnetic charges, and the 'accessible' energetics in the system is thus rightly attributable to magnetic not electric interactions. As per both #45 and #61, there is a minor additional contribution owing to induced eddy currents in the media. These do conform to electrical E.j type interactions, but are typically tiny wrt the main magnetic energy changes. That's my piece repackaged, and I welcome any constructive critique. Must go. :zzz:

 

[cabraham]

These threads can be effective at getting us to think deeply about science & expand our understanding. Unfortunately, there are always people who force fit everything into their preconceived narrow view of the world, & think the world should adopt their viewpoint because it is "right". They use words like "fundamental", "such and such can NEVER do work", etc.

I am now convinced that there are those who refuse to accept that B forces can do work despite evidence to the contrary. They spin everything & change rules at will just to suit their foregone conclusion. The final answer is simply that under dynamic conditions E & B always coexist mutually. You can never have one w/o the other.

Energy is transferred in & out of both of these fields. Both are doing energy transfer, but depending on the conditions, one of them may be what provides force & hence that quantity is doing work. But the other is supplying energy & without that other field/force, it would not be able to do work alone because they are mutually inclusive.

So when we say that E does work, or that B does work, it's too easy to say "no, it's the other one doing the work" because conservation of energy is immutable. Without the other, well, just forget it.

So can B do work lifting a magnet or paper clip? The naysayers have provided equations & arguments saying no, but I find an inconsistency in their position worth highlighting.

Lorentz force is agreed upon as being all important. It has 2 components, Fe due to electric force, & Fm due to magnetic force. We know Fe = q*E, & Fm = q*(uXB). So why is it that E can do work, yet B cannot do work? The classical naysayer answer is that E can act in the direction of motion, but cannot. B acts normal to motion & thus cannot do work, since B only can change a charged particle's momentum, but not its KE.

Personally, I agree with that. If a force acts in a manner on an entity such that it is not aligned with the entity's motion/path, then that force cannot be what is doing work. This is why an electron moving through a B field & an E field incurs a change in KE due solely to E, not to B. Its momentum change is due to both, but its KE change is due entirely to E. So far I really doubt that anyone would dispute me.

But when a magnet lifts another magnet, which force is doing the work, B or E? In the motor thread I provided sketches, but this is the magnet thread. So I ask this, which field, B or E, is along the direction of the moving magnet as it ascends? That field is doing the work. In the motor thread, the B force was along the rotor motion so it had to be doing the work. Can somebody provide a sketch of the magnetic forces & their orientation? My sketches do not seem to convince them. Without drawing the forces out, I cannot be sure, but it sure looks like B forces do the work lifting the magnet. Again, if that is not the case, I just ask that you sketch the vectors showing how the E force acts in the vertical direction. Thanks in advance.

Claude

 

[Dale]

His first post is the main conclusion. It's the same as the preview thread that I've started, unfortunately Dale and I disagree. I honestly do not believe that the same concept on a "loop" is applied to a "permanent magnet".

Can you cite any peer reviewed evidence showing that Maxwells equations do not apply to a permanent magnet? If not, then on what do you base your belief?

 

[Dale]

To claim E.j work is being done on such intrinsic moments is inviting a severe paradox since, as touched on in #26 "there must somehow be some mysterious energy source which keeps the magnetic dipole moment constant when subjected to external field," (actually, time-changing B field giving rise to non-zero E.j)

And your evidence for this is ...?

 

[Dale]

What evidence's do you need? Dale, the basics of all of this is that magnet's certainly can do work. What exactly is doing the work? I find that difficult to prove.

Then you should look at the proof I provided. It is not that difficult, and once you understand it you see that it applies to all of classical EM.

Iagreed earlier that magnetic fields/forces do work but INDIRECTLY to a loop of wire. However, in case of a magnet things would totally differ here.

How so? Which of Maxwells equations are violated for a magnet?