Im curious about magnets... Can they be a source of energy or not?

  1. Greetings fellow members!(New guy!)

    Before I would start, I've already read a lot of the threads related to "magnets" and "energy". I do undertand the PF forums rules. So please don't lock this thread and say "THIS IS NOT ALLOWED" in reality it is... But maybe its because of the unfortunate reason that this topic attracts many "crackpots". However, that shouldn't effect me or others to learn? should it?

    I've had my share of reading those posts and understanding the reasons why. But here I come to be enlightened about an idea, that is really popular as you all may already know...
    I do not have any intentions to speak about Perpetual motion, this is not related to it at all... Although the irony is that many have used magnets for that blinded and ignorant reason. And gave it an "X" mark for further discussions, hasn't it?!

    So as a layman here who's really studying basic physics in hopes of becoming an engineer soon! Could you please describe to me why magnets can NOT be a source of energy? In any way?

    Again a source of energy that changes or becomes less/weaker/converted/etc... In due time, with respect to the laws of conservation AND thermodynamics.

    I have a set of arguments, and my mind just can't stop of this idea, so I'd like this to die from your reasons and I can move on!

    Please I ask of all the Admins + Mentors to give me a chance to learn!

    Thank you.
  2. jcsd
  3. mfb

    Staff: Mentor

    What exactly do you consider as "source of energy"?

    - you extract energy, and the system remains the same? That is impossible, you can derive energy conservation from the laws of electromagnetism (Maxwell equations). There is no possible way you can change the total energy.
    - you extract energy, and the system lost energy which was stored in magnetic fields? That is possible, and done with coils all the time.
  4. I'm not sure what you mean by source of energy also. My guess is though that you understand what mfb is saying about coils. Generators use magnets to convert rotational mechanical energy into electrical energy, and in reverse a motor converts electrical energy into mechanical energy. I've heard about people using the earths magnetic field to produce "free" energy, but still the rules of conservation of energy would apply.
    You should elaborate if you are envisioning something else.
  5. OmCheeto

    OmCheeto 1,869
    Gold Member
    2014 Award

    Because they are equivalent to springs.

    Springs being like that tiny coiled thing in the end of your pen, that pushes that pointy thing back into your writing utensil.

    You can click, and click, and click all day, but you'll never do anything useful. Really...

    You are welcome.
  6. russ_watters

    Staff: Mentor

    Or another way: is a spring a source of energy?
  7. So far I know an energy source, is an object or system that gives off an excess of energy.
    Why is it that magnets are compared to springs? I find that magnets are more complex.
  8. How is it that Maxwell's equations proved that magnets are not capable to be a source of energy? Could you all give me examples(analogies) with magnets?
  9. OmCheeto

    OmCheeto 1,869
    Gold Member
    2014 Award

    Magnets are more complex. I would explain how they work, but after going on a roller coaster ride in another magnet thread, I've decided that I have not a clue how they work.

    And I compare them to springs, because, well, when you pull or push magnets together or apart, something feels springy.
  10. mfb

    Staff: Mentor

    Without losing energy? In that case, there are no enery sources at all. All you can do is transform energy between different types.

    An example of energy conservation?
    - Do nothing, nothing changes.
    - Shoot electrons through a static magnetic field - they change their direction, but not their velocity (and therefore their energy).
    - Put two permanent magnets on a table and let them attract each other. Some part of the energy stored in the magnetic field will be converted to mechanic energy (if they approach each other) and later to heat (if they crash into each other).

    If you are interested in mathematical details, check this pdf or Poynting's theorem, for example.
  11. BruceW

    BruceW 3,532
    Homework Helper

    I totally agree with mfb on this one. There are no energy sources. (Except maybe if you think about general relativity, in which energy is not globally conserved. But even then, it is locally conserved).

    All you can do is turn one kind of energy into another. For example, we dig fossil fuels out the ground and burn them, we are turning some of their chemical energy into light and heat. If this is the kind of thing you meant to say, then yes, you can take energy from the electromagnetic field and turn it into another kind of energy.

    In fact, chemical energy is really just energy stored in the electromagnetic field. So in a very real sense, we are taking energy from the EM field all the time. But specifically about magnets, it is hard to think of a situation where you could de-magnetise the magnet, to turn that energy into some form of energy which is even slightly useful. I would guess that usually the energy just gets converted into useless heat.
  12. LOL, no wonder you've been awarded for your humor! Besides that... From that post, I really realized how complex magnets are, yet they seem so simple!

    Your right. The term "energy source" is wrong.
    But I'm not looking at the interaction of an electron with a static B field. But rather a dipole(Permanent or electric). Simple way to put it two bar magnets have potential, if their magnetic fields are interacted to each other (depending on the poles) it would apply a force of attraction or repulsion and would cause motion (KE) so simply a conversion of PE to KE.

    True, basic energy conservation.
    "But specifically about magnets, it is hard to think of a situation where you could de-magnetise the magnet, to turn that energy into some form of energy which is even slightly useful."

    Indeed, I believe that would require a lot of effort and study to find out something useful, its known that hard and complicated issues would lead to great outcomes sometimes.
  13. mfb

    Staff: Mentor

    Well, you get some conversion if you put two magnets on a frictionless surface and let them attract/repel each other. A small permanent magnet has a very limited energy, however: 1 T corresponds to ~400 kJ/m3 or 0.4 J/cm3. With 1 T in a volume of some cm3, you get some Joule of energy in the magnetic field.

    As comparison, petrol has an energy density of ~35000 J/cm3 and even hydrogen gas at atmospheric pressure has 10 J/cm3 chemical enery (if burned with oxygen).
  14. russ_watters

    Staff: Mentor

    Magnets aren't really more complex than springs, they just seem more mysterious, but that is only because the fact that you can see a spring tricks people into not looking deeper. But they act fairly somilar, particularly as a demonstration of conservation of energy:

    A magnetic oscillation, spring, pendulum - all demonstrate conservation of energy in similar ways. None can have energy extracted from them.

    And springs when you look deeper become more complex, since they are complex collections of lots of little magnets in complex arrangements.

    Also, though people often think generators extract energy from the magnetic field, even if they did, the amount of energy would be so small it could still be ignored in the operation of a generator.
    Last edited: Dec 25, 2012
  15. DaleSpam

    Staff: Mentor

    A magnet has a magnetic field. The magnetic field has an energy density which is proportional to the square of the magnitude of the magnetic field.

    Consider a dipole magnet in a uniform external field. When it is arranged parallel to the external field then its field adds to the external field, increasing the total energy stored in the field. When it is arranged anti-parallel then it's field subtracts from the external field, reducing the total energy stored in the field. Energy can therefore be extracted during the transition from parallel to anti parallel. But once it is anti parallel work must be done in order to turn the magnet.
  16. OmCheeto

    OmCheeto 1,869
    Gold Member
    2014 Award

    [John Merrick voice]
    I, am not, trying to be funny. I, am, a scientist!
    [/John Merrick voice]

    This is already over my head. I don't know why I'm attracted to magnetic threads, but I am.



    ps. I will try not be be so funny in the future.
    Though, with the badge hanging around my neck like an elephant tied to the end of my noose, I somehow feel like the humor police. "You will.. respect you authoritay(sic)...."
  17. This is the feature that misleads so many about magnets. The field is invisible and has no effect on any human sense. Yet, when you try and push like poles together you can feel the most mysterious resistance, as if they are shooting some energy at each other, or at least expending some energy in creating a force field to repel each other.

    There's a real field around both magnets, to be sure, but what isn't apparent is that the fields are completely static and do not require the expenditure of energy for their existence. The force you feel is just the force of you pushing one hand against the other; the same as you would feel if you tried to push two rubber balls together, or two bricks for that matter. It's just like gravity in the sense it's a force that requires no expenditure of energy for its continued existence. You can store energy in both but neither amounts to a "fuel". A magnet is as much a source of energy as a brick.
  18. berkeman

    Staff: Mentor

    What a waste of time. Thread closed and OP PM'ed.
  19. berkeman

    Staff: Mentor

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