Why are magnets debunked when talked as a source of energy?

Discussion in 'Physics & Math' started by Believer99, Feb 23, 2013.

  1. eram Sciengineer Valued Senior Member

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    PhDs acting like 12 year olds or 12 year olds pretending to have PhDs?

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    That's cool.

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    I'm considering going into engineering.
    Is Aerospace really difficult? And with thermo and fluid dynamics, what sort of industry do you work in?
     
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  3. leopold Valued Senior Member

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    so this phenomena is more pronounced with a coil/core.
    furthermore this setup must be lossless and perfect, correct?
    i agree that under perfect conditions you can get the APPEARANCE of more power with a coil/core.
    it's directly due to the magnetic field the coil generates.
    it's also a "handoff" situation where the "power" is handed off to the coil and core respectively.
    at a certain frequency this handoff becomes in phase with each other and you have resonance.
    the capacitance of this circuit is the distributed capacitance of the coil which will be small which means a high resonance frequency.


    it IS relevant.
    there's theory and there's application, they don't always jive.

    i don't know.
    i can't see how a static magnetic field can do anything unless there is some kind of conductor moving through it.
     
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  5. Q-reeus Valued Senior Member

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    Despite every effort it's just not been getting through to you (or anyone else it seems). The core phenomenon - where it's all at in effect, has nothing to do specifically with the surrounding windings. In the toroidal 'inductor' scenario, sole purpose of said windings is to generate an applied B field. It's very convenient and useful that in that toroidal geometry, what's known as the demagnetization factor for the core media is zero. Which helps much to simplify and make for a 'clean' analysis of the physics.

    An essentially equivalent scenario could have been presented where only permanent magnets were used to establish an applied B. But typically one then needs discussing effect of demagnetization fields. Because permanent magnets cannot generate a toroidal shaped field so specimen will be some other shape than a toroid and it gets messy. Positing a very thin wire of magnetic media is one way around that difficulty, as demag factor asymptotically approaches zero in that case. Just never anticipated chosen toroidal scenario would generate so much continued confusion.
    For the umpteenth time - NO! Any more than gears or pulleys or levers or bearings need to be absolutely friction-free to work! Recall that high school physics lesson where the principle of the ramp or screw was first introduced? Remember - one takes force components - sines and cosines and tangents and all that. One rightly ignores friction in order to isolate the principle of the ramp or screw. Nothing sneaky or underhanded going on. An engineer will often need to take into account losses in a real world design situation, but none of that negates the underlying principle being exploited. Which is only cleanly revealed by taking the idealized, frictionless case first! And the same general story carries over into electrical systems - one works with ideal inductors, capacitors etc. in order to establish basic principles. Later one introduces the non-ideality of real components, but none of that negates the underlying basic principles established by use of idealized linear and/or lossless components. Getting the idea now?
    How many times already has it been said, beginning back in #35, then #44 and so on - AC power factor and/or resonant phenomena has exactly zero relevance to #19 and later posts. Zero! And the rest of that piece I have either covered above (yet again), or cover below.
    Very obviously you're not seeing it. But it's all explained back there in #19. For whatever good it may do, here's a recap of sorts:
    A uniformly magnetized specimen of ferromagnetic material, say an axially magnetized cylindrical rod, can be treated as though a solenoid carrying a uniform surface current density - termed magnetizing or bound current density Jm. If the applied external field Be, of whatever source, solenoid or permanent magnets, is sufficient to fully magnetically saturate that rod specimen, then any further increase in Be to say Be + dBe has no effect on Jm which remains fixed. Which is interesting since by the Maxwell-Faraday's law, that increase in Be to Be + dBe induces a back emf and associated circular electric field E. That attempts to reduce Jm so as to keep the rod internal magnetic field strength, thus magnetic field energy density constant. This cannot happen in the case of saturated media - Jm stubbornly resists (via quantum mechanics!) any attempt at reducing. As though some internal source of emf was acting to counter that owing to the time-changing Be. But there is no such internal battery! Net system energy by this account has changed precisely in the amount given by integrating -E.Jm over the volume of the specimen of media, and over time involved in going from Be to Be + dBe.

    We do not need in this approach to worry about the energy expended in the external field supply - whether involving currents in coils or forces in moving magnets about. Wholly and solely the net system change is given by the time integration of product of minus the back emf times bound surface current
    [Edit: Not strictly true in the case PM's are external B source, since we must expect mutual interaction between such PM's to cause a similar change in internal energy. What can be said in that case is the sign of any such PM-PM mutual interaction internal energy is the same as that applying to the saturated specimen lying in between. This is easily argued qualitatively based on net change in demagnetization field. So overall result additive but exact figure difficult to calculate. If solenoidal coil(s) is source of applied B, no such complication exists]].

    In #19 I used a different but equivalent approach in terms of field energy densities. [Exploiting this excess energy requires a cyclic procedure as per last part of #19 - but the core phenomenon allowing that exploitation is as presented (again) above. And again - it's a very weak effect owing to mass/inertia change - not electrical feedback!]

    Now if there is some physically plausible mechanism that somehow exactly compensates for this net system energy change, I have no idea where it can be pulled from. And would be fascinated to hear of a genuine attempt to show such. So far no-one here has even tried, nor do I expect after so long now it will be forthcoming. But surprises can happen. :bugeye:
     
    Last edited: Mar 8, 2013
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  7. Reikool Banned Banned

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    no the static magnetic field has an effect on charged particles even if they are not conductive material
     
  8. billvon Valued Senior Member

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    Once a material is saturated it neither 'resists' nor 'encourages' additional flux density. It is saturated and thus does not add any additional permeability to the system. mu drops to mu zero, the permeability of free space. Thus additional magnetic field is not kept constant; it simply rises at the same rate you would see if there was no core there. There is no "resistance' to additional field.

    You can verify this by looking at the B-H plot of a ferromagnetic material. At saturation B does not stop rising; it just rises very, very slowly compared to H.
     
  9. billvon Valued Senior Member

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    Only if the charged particles are moving. A static charge does not interact with a static magnetic field.
     
  10. Q-reeus Valued Senior Member

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    Agree entirely with that bit (perhaps not quite the wording "does not add any additional permeability to the system", but I get the meaning there). If you read #19 carefully all above points are stated there. You seem though to be implying I say otherwise in passage you quote, and it's not so. In saying there is 'no change in magnetizing/bound current density Jm' with changing Be, that automatically implies the net field must change. Just check how I arrived at expressions (1) and (2) in #19! One can express and calculate the claimed excess internal energy either in terms of fields, or power/energy required to maintain the bound current constant. They give equivalent results.
    Note btw I have edited (what is now) 3rd last para in #183 re PM mutual interactions.
     
  11. leopold Valued Senior Member

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    you know, i keep thinking they labeled tesla as a nut too when he spoke of death rays from space.
    truth is he was the reigning genius of the times.
    industrial power and its transfer is directly attributable to this man.
    his lab was finally dismantled and most of his research fell under US classification.
    he was also dealing with what is being discussed here.
    so, does she or doesn't she?
     
  12. leopold Valued Senior Member

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    17,455
    i think you need to figure out how to extract power from the earths field.
     
  13. leopold Valued Senior Member

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  14. Q-reeus Valued Senior Member

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    There is a persistent cult following for Nikola Tesla, and I had always dismissed it as essentially all hype and myth. Just recently though came across some very interesting material on his work and now have much more respect for what he achieved and do puzzle over how he managed to pull off certain feats. His thinking certainly wasn't conventional in many ways.
    Huh?

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  15. Q-reeus Valued Senior Member

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    If you mean the magnetic field, well apart from a slow variation that is constantly monitored, it's quite weak and just 'sits there'. What I did look into briefly was the feasibility of appreciably extracting earth's rotational energy via a certain resonant gyroscope configuration. But others have looked at similar schemes and it always comes up looking somewhat disappointing. [that's a euphemism for saying it can't work at all - conservation of angular momentum get's in the way. A one-off reshaping of the earth would 'do the trick', but hardly practical to try.]
     
    Last edited: Mar 9, 2013
  16. Aqueous Id flat Earth skeptic Valued Senior Member

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    And why is that? Just come out and admit that the static field is not in itself a source of energy.
     
  17. river Valued Senior Member

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    Geologically though....friction
     
  18. Q-reeus Valued Senior Member

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  19. Q-reeus Valued Senior Member

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    Talking to me? It's ignorant not to quote, but that's in keeping I guess. How about you admit that vacuous comment is skew of last post's topic and anyway you are proven incompetent to judge anything on what I'm on about. And btw It would have been easy to tear apart every one of your reply comments here:
    http://www.sciforums.com/showthread...ce-of-energy&p=3049501&viewfull=1#post3049501
    but I chose to let it go. Seems you just can't. LET IT GO NOW!
     
  20. Maximum_Planck Registered Member

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    I think your right. Static field cannot have self-energy source because vacuum fluctuations do not permit virtual pairs from forming before the energy is extracted.
     
  21. Q-reeus Valued Senior Member

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    A perfectly static field obviously cannot by definition be a source of further ongoing energy. And that obvious truth has been used as a phony argument that is completely skew of what I have been writing about. Chalk and cheese. Always in my scenario, change is involved. Always. Be careful about mixing in talk of virtual pairs and the like here - none of this 'energy from the quantum vacuum stuff' please.
     
  22. leopold Valued Senior Member

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    i am more confident than ever that your setup is somehow using the apparent power that the above mentioned changes produces.
    you say this setup works solely with a PM but you are neglecting the "shorted turn" scenario.
    with a PM this shorted turn is the PM itself.

    yes, your setup will indeed produce the appearance of power, but only as long as you have relative movement between the field and PM, or the field and the coil/ core.

    edit:
    since a PM isn't optimized against eddy currents some, if not most, of this power will be lost by heat, it will get quite warm depending on the fluctuations of the field.
     
    Last edited: Mar 9, 2013
  23. Aqueous Id flat Earth skeptic Valued Senior Member

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    Yes, in a world where ferromagnetic materials are "fundamentally quantum mechanical in nature" I suppose all of your conclusions are correct, including this one.

    Tear away.

    What have you let go of? The rope you think I'm holding is merely anchored to the ground. You're tugging against reality, not me.

    Does that mean you agree that a stationary solenoid immersed in a static magnetic field cannot generate electricity?

    By "change" do you mean energy must be supplied, in an amount greater than the amount that can be converted to useful work?
     

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