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

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

  1. Believer99 Registered Member

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    So give me those reasons.
    Why?
    Why cant someone say that I'll study magnets and hopefully produce a source of energy from them without getting debunked.
    I would blame the idea of perpetual motion being backed up by magnets constantly, and all the realm of fee-energy.
     
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  3. origin Trump is the best argument against a democracy. Valued Senior Member

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    Since magnets are used currently in generators that produce electrical energy, I think it is impossible to debunk them as a source of energy!
     
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  5. billvon Valued Senior Member

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    Because they are not a source of energy, just a source of magnetism. They can be used during the generation of energy of course.

    Water can be used to generate energy when it falls over a dam. Does that mean that water, all by itself, can be a source of energy? Nope, it's just a carrier of potential energy.
     
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  7. rpenner Fully Wired Staff Member

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    There are two things about energy and magnets. One is that the energy associating with any number of magnets is a conservative field expressed in the relative location of the magnets and their orientation. Thus every pair of configurations of magnets has an associated energy difference, so if you have a cycle -- no matter how complicated -- it eventually returns to a configuration state we have seen before and the energy difference is zero.

    Two: Permanent magnets aren't permanent but are arrangements of microscopic dipoles. There are a few devices which extract the energy of permanent magnets, shifting their configuration to a lower energy state and converting the difference into electrical or mechanical work. But as the energy of magnetization of a permanent magnet is quite small these are not perpetual motion machines and the derangement of the microscopic magnets is just a special case of the conservative field configuration -- eventually you can't derange the permanent magnet anymore and your cycle is again cycling through the same energy states as before with zero power out.

    // Edit:

    Three: (Not a point about magnets, per se). We have, in special relativity, a complete description of how much energy may be extracted from any closed system. Take two identical boxes. Put the system in one of the boxes. Measure the mass difference between the boxes, \(\Delta m\). Thus the maximum energy that can be extracted is \(\Delta E = c^2 \Delta m\) which means that any claimed self-contained perpetual motion machine isn't. (For chemical reactions, the amount of mass loss in exothermic reactions is no more than on the order on one part in a trillion billion; for magnets extracting work from other magnets, even less -- so this is not a practical way of determining the limit, just an argument from fundamental physics that a limit exists.)
     
    Last edited: Feb 23, 2013
  8. Aqueous Id flat Earth skeptic Valued Senior Member

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    (adding to origin's remark):


    Yes indeed. The magnet, once it's set in motion by another energy source, makes a good source of electrical energy

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    .

    That just leaves us to debunk the nutty belief that no energy has to be put into the generator.

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  9. AlphaNumeric Fully ionized Moderator

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    It is not uncommon for people to think "If a magnet can stick to the side of my fridge isn't it using energy? Where does that energy come from?". This is a mistaken line of thinking because the magnet isn't using any energy as it isn't moving against a force, it is still. Our arms get tired if we dangle from a bar because of the way in which chemical processes provide our muscles with energy so when you stop dangling and feel your arms are tired it is not because you expended tons of energy fighting gravity, you didn't, but rather its a build up of various stuff in your muscles.

    If magnets spontaneously slid up a fridge door then it would be doing work by moving against gravity. Just sitting there it does nothing, just like you don't have to expend any energy fighting gravity when you're lying in bed. Unfortunately too many people conflate the imperfect way our bodies deal with energy with something fundamental about energy conservation in physics.
     
  10. Russ_Watters Not a Trump supporter... Valued Senior Member

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    I usually just answer with a question: is a spring a continuous source of energy or just temporary storage?
     
  11. leopold Valued Senior Member

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    magnets can be used as a source of energy.
    keep in mind that so far perpetual machines have not been possible.
    some keep trying though.
     
  12. billvon Valued Senior Member

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    No, they can't - any more than a gallon of water can be used as a source of energy.
     
  13. AlphaNumeric Fully ionized Moderator

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    Not in the sense perpetual motion machine use. There is energy in the magnetic field due to the configuration of the magnet's atoms, much like lining a bunch of dominoes up has some energy as a result. However, that energy cannot be removed from the magnet without removing its macroscopic magnetic properties. It is like saying something which is hot has energy. Yes, but when you make use of that energy you drain it from the system and make it cool.

    It is impossible to design a perpetual motion machine based on the Maxwell equations for electromagnetism because Maxwell's equations lead to energy conservation. As such the only way to do it is to not use current models, you'd have to develop a novel model of electromagnetism which doesn't always conserve energy.
     
  14. Aqueous Id flat Earth skeptic Valued Senior Member

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    Only figuratively speaking. Not in the literal sense.

    Perpetual motion machines will never be possible for the same reason they're not possible now.

    In vain, with nothing more than cynical naivete to guide them.
     
  15. Pete It's not rocket surgery Moderator

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    10,166
    Why are hall tables debunked when talked as a source of energy?

    So give me those reasons.
    Why?
    Why cant someone say that I'll study hall tables and hopefully produce a source of energy from them without getting debunked.
    I would blame the idea of perpetual motion being backed up by hall magnets constantly, and all the realm of fee-energy.
     
  16. billvon Valued Senior Member

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    Because they would be wrong. It's like asking "why can't someone say they'll just go faster than the speed of light without getting debunked?" Because they can't. Magnets are not a source of energy. Period.
     
  17. Pete It's not rocket surgery Moderator

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    Sure, but I'm talking about hall tables, not magnets.

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  18. billvon Valued Senior Member

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    The Hall effect is just one of the many effects that magnetism has. Again, not a source of energy.
     
  19. BdS Registered Senior Member

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    How would you describe a magnet picking up a ferrous object when only its field comes in contact with the ferrous object and the ferrous object moves up to the magnet? Didn't the magnet create a force (requires energy I think) in the ferrous object since it moved it against gravity?

    Just curious how you would explain this scenario.
     
  20. AlphaNumeric Fully ionized Moderator

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    In that case there is potential energy stored in the system, in the same way a brick sitting on a table has stored energy. When you move the brick to the edge of the table it goes into an unstable configuration and converts that potential energy into kinetic by falling to the floor. Likewise with the magnet. There is potential energy in the separation of the magnet from the metal object. When you move them close enough the configuration becomes unstable and it is energetically preferable for the magnetic potential energy to be converted into gravitational potential energy (ie the magnet lifts the object). The magnet doesn't contain the energy, the energy is contained within the configuration of the objects. To then use this energy again you have to use your arm to pull the objects apart and put them back in their initial positions. Your arm provides energy which goes into magnetic potential energy again. Then when you use the magnet to lift the object you convert that energy back into kinetic and gravitational energy.

    Objects which create forces, be it gravitational due to mass or electromagnetic due to charge, do not contain energy in and off themselves in that way but rather their relative position to other objects which feel said force is what stores the potential energy. An object in space has gravitational potential energy relative to the Earth, moving closer releases kinetic energy and moving them apart requires energy from a rocket or other propulsion device.

    As my previous post mentioned, magnets can contain energy due to the alignment of their atoms but this is another example of potential energy. A fros material becomes magnetic if you align the atoms properly. This requires energy to do so because you have to set them in a configuration they would prefer not to be in but they cannot move out of because of the metal's atom arrangement being fixed. If you heat a magnet to its Curie point you give the atoms enough kinetic energy to be able to realign themselves and they prefer to point in different directions, not all the same, and when they do this the metal is no longer magnetic (or becomes much much weaker at least). In this case you put the system in a configuration where it is energetically favourable to slide into a new configuration, just like pushing a brick off a table or picking up a paper clip with a magnet.
     
  21. leopold Valued Senior Member

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    17,455
    am i missing something?
    a gallon of water can provide a lot of energy when separated into oxygen and hydrogen.
    okay, i see what you mean.
    the spring analogy is a good one too.
     
  22. Q-reeus Valued Senior Member

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    2,497
    I may regret this, but rather than keeping quiet or starting a new thread on it, will dive in here and risk opprobrium from the luminaries here at SF that have passed judgement on this subject and are thus committed. Some time back in another forum, I tangled with some heavyweights on the matter of permanent magnetism. In challenging the repeated claim, backed by such authorities as J.D.Jackson and D.J.Griffiths that work done on and by magnetic media is always of the electrical E.J type, could not get a single one there to back that up given the nature of an intrinsic magnetic moment. Anyway an aside was I gave repeated oblique hints of a sleeper issue evidently not so far recognized in all that. No-one bit then so let's see how it goes here. Will keep it descriptive.

    The one key thing about ferro or ferri magnetism is it's fundamentally quantum mechanical nature. Especially in ferromagnetic media such as iron, it is almost exclusively owing to the contribution of electron intrinsic magnetic moments, with negligible orbital contribution. Once all the magnetic domains and hence constituent intrinsic moments are fully aligned we have magnetic saturation, and further increase in applied magnetizing field has negligible effect and for all intents and purposes the media has a susceptibility arbitrarily close to zero. That's owing to that an electron intrinsic moment can only have the single magnitude of μ defined for instance in the Wiki article here: http://en.wikipedia.org/wiki/Electron_magnetic_dipole_moment

    There is strictly a tiny further increase even well beyond point of nominal magnetic saturation but it is really tiny and not of consequence to what follows.
    One of the two popular ways of modelling magnetic media is as a conglomerate of 'true magnetic dipoles' formed from fictitious magnetic monopoles - leading to the Gilbert model that talks in terms of surface charges and scalar potentials.
    The other one is the Amperian model where magnetic dipoles are considered to be tiny perfectly conducting loop currents, and here one talks in terms of fictitious surface magnetizing currents and magnetic vector potentials.

    Turns out from cosmic ray deflection experiments performed in the 1940's and later by neutron deflection experiments carried out in the 1950's, the true fundamental behavior of magnetic media conforms to the Amperian not Gilbert model in at least one important respect. High energy thus penetrating particles deflect as though a permanent magnet was throughout a solenoidal source of B field, not like the magnetic equivalent of an electret comprised of 'impenetrable dipoles' a la Gilbert model.
    On the other hand, the Amperian model of classical loop currents cannot explain why magnetic media should be other than weakly diamagnetic in accordance with Lenz's law, and the Gilbert model of fixed magnitude rigid dipoles is much better at explaining e.g. magnetic saturation, at least on a gross-behavior level.
    One could say the true situation involving principally intrinsic moments can be thought of roughly as a hybrid of the two.

    So where is this leading? Consider the case of a superconducting toroidal solenoid - sts for short - snugly enclosing a similarly shaped toroidal loop of ferromagnetic magnetic material - tfm for short. For simplicity have that minor toroid diameter is small relative to major diameter, hence little variation from an average value of field strength within sts and tfm will hold. We suppose the tfm is composed of something like Supermalloy that relatively sharply saturates to some field value Bs at a very low applied B field B1 owing to a supercurrent flowing in windings of sts. This magnetization procedure all takes a certain amount of input energy into sts and there is no obvious hint to this point conservation of energy fails in the least.

    Ask though what is 'internally' the energetics when say applied field B2 >> B1, i.e. way above saturation point, with effectively zero susceptibility in tfm. Owing to that near enough to zero susceptibility, incremental input energy into sts required in going from say B2 to B2+dB is just that of an equivalent 'air-core' sts with no tfm media within. That is
    dW ~ (B2+dB)^2 - B2^2,
    ~ 2B2*dB + dB^2
    ~ 2B2*dB - (1) (for B2>>dB)
    But there is media present, and despite essentially zero inductive feedback as per Faraday's law, the net internal field, in accordance with previous discussion, is the sum of applied B from sts and saturation magnetization field Bs owing to sfm. Hence the actual net magnetic field energy change dW' will be
    dW' ~ ((B2+Bs)+dB)^2 - (B2+Bs)^2
    ~ 2(B2+Bs)dB + dB^2
    ~ 2(B2+Bs)dB - (2) (for (B2+Bs)>>dB)

    Which is clearly greater than for (1), perhaps very much greater since typically for a good Supermalloy or certain even better glassy metallic media, Bs can exceed B1 by a factor of tens of thousands easily, and still by a factor of thousands for some reasonable value of B2. (sorry about using B everywhere instead of using H for magnetizing field, but it saves putting in added symbols in above)

    And just where has all this extra energy magically come from you may snort. Well imo it comes from the 'magical' fact that an intrinsic moment is radically different to the Amperian classical loop current in that Faraday's/Lenz's law just fails utterly. If the tfm had behaved as an agglomerate of classical Amperian loop currents, Lenz's law would ensure the internal net field B2+Bs+dB was essentially constant - implying zero self-inductance for sts windings and something clearly at odds with actual behavior. In that other forum I compared it to what happens when one steadily shrinks a superconducting loop in size. At first, for macroscopic size range, behavior is essentially that of an equivalent perfectly conducting classical Amperian loop current. Lenz's law holds no sweat and essentially perfect diamagnetism applies. But start getting down to the point where fluxoid quantization noticeably bites (see http://en.wikipedia.org/wiki/Magnetic_flux_quantum) and things get somewhat 'jerky'. As loop enclosed area shrinks, so rises the step width over which applied B changes before a discontinuous jump in supercurrent transpires. Taken to the ultimate limit one arrives at something looking suspiciously like an electron intrinsic moment - for which no step in moment is possible regardless of applied B value. Lenz's law* no where to be seen at this level. Which kind of makes Poynting theorem arguments a little suspect imo. [*Edit: Earlier wrote Faraday's law instead of Lenz's law above - latter was always meant. The former of course always holds, but it's manifestation as emf associated with a time-changing applied flux fails to induce a classical response in saturated media]

    It's the case actual electron intrinsic moments are within the media lattice structure experiencing gyromagnetic precession which leads to an effective moment less than the intrinsic one. And which can to some degree respond by changing in an applied B. Nevertheless in practice the internal domain fields 'pin' such change to an ineffectually low level given the sort of modest applied field values relevant to above scenario. As witnessed by the actual B-H curves and saturation behavior in ferromagnetic media (see e.g. http://www.magmet.com/tapewound/magnetic.php). Net macroscopic model for tfm well above saturation is then of a solenoidal magnetizing current mysteriously immune to Lenz's law. Somehow a quantum mechanical 'internal voltage source' is acting here - opposing precisely the emf induced when current in sts is changing so as to change e.g. B2 to B2+dB. And doing so I humbly suggest quite 'free of charge'. Note carefully though, this extra energy is of the internal kind. No way to directly electrically extract any such excess energy by way of a half-way clever cycling of the energizing supercurrent in sts.

    However, there is another way or rather range of ways - nothing that will set the world on fire but there in principle. That internal excess energy surely acts normally in the sense of having a relativistic mass/inertia. So this immediately suggests any number of cyclic schemes that involve wholesale motion of the assemblage.

    One example: Raising and lowering assembly against gravity, with lower solenoidal current during rise part, higher during lowering part. It should be obvious how that cycle is nominally at least gaining energy each time. We of course idealize to a lossless process driving the supercurrents up and down, but it's not some critical requirement here. I see no credible mechanism that would nullify via a concomitant coupling of solenoid supercurrent in sts to gravitational potential, but I expect some here will be searching for just that.
    Another one: Similar to above but horizontal reciprocating motion - i.e. taking advantage of a variable inertial mass. And various other schemes are not hard to dream up - once the initial thought is in place that is.

    None of the above meets any kind of rigor a real boffin will demand. Understood. Still I believe it's reasonable to expect the onus is now on the rest here to point out any specific physical implausibility in above. Not by merely claiming it violates fundamental symmetry principles etc. Oh my this posting has grown like topsy! Ah well, what the heck -go for it folks. Will be back much later to see what turns up!

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    Last edited: Feb 25, 2013
  23. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Did you read my post about springs? A magnet pulling an object toward it is releasing potential energy. Pulling the object off it requires putting back into the system exactly the same amount of energy as was released.
     

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