Energy in a magnet

Discussion in 'General Electronics Chat' started by mentaaal, Dec 22, 2007.

  1. mentaaal

    Thread Starter Senior Member

    Oct 17, 2005
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    Hey guys, you know the way that say for example a magnet could attract a metallic object to itself. Say for the purpose of this question, a magnet attracts a nail to itself in a vertical plane and thus defying gravity. As work needs to be done and energy transferred to do this, where does this energy come from? I mean its from the magnet but how does this energy get lost from the magnet and how is this energy loss manifested, as in what effect does this energy loss have on the magnet?

    Thanks guys!
     
  2. Salgat

    Active Member

    Dec 23, 2006
    215
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    My guess is that it slightly scrambles the arrangement of the poles in the magnet. Making magnets requires quite a bit of energy.
     
  3. okie

    New Member

    Dec 21, 2007
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    Salgat, I think you're right. When the nail moves toward the magnet, according to Maxwell's equations, there's current induced in the nail, which results in an opposing magnetic field. This field would have an effect on the little molecules or atoms with dipole moments in the magnet, and they'd each have some chance of being knocked the other way.
     
  4. boltcutter

    Member

    Dec 5, 2007
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    I'm no Physics person, but I'm not sure you guys caught on to the original question. Seems like you were referring instead to the longevity of the magnet. Isn't the energy question resolved when one tears the object away from the magnet again? Isn't the work question resolved once the magnet and whatever it's attracting are in a steady state? Anyway, those are my non Physics person guesses.
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
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    I think I tried to find the answer to that and failed. I think you're right, removing the object 'recharges' the magnet. They will fail as the transfer is not perfect though.
     
  6. recca02

    Senior Member

    Apr 2, 2007
    1,211
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    My guess is(this is a bit hard to think n accept ):

    the nail or whatever was initially at some potential with respect to the magnet(i think theoretically a nail in my country wud still be at some potential with respect to magnet in US:eek:).
    this work was done by nature(how it got into this configuration - god knows) initially.

    now this work stored as PE of the configuration tries to get into a static equilibrium or a position of lesser PE this work then manifests itself as Ke of the nail or magnet or both.
    what say?

    in any case i think the above replies do have something to do with the answer too but it wud require to delve a lot deeper into the subject.
     
  7. chesart1

    Senior Member

    Jan 23, 2006
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  8. mentaaal

    Thread Starter Senior Member

    Oct 17, 2005
    451
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    We are doing maxwell's equations next year... I'M SCARED!
    I had a look at that link... but i think to grasp it i am going to need to be studying the topic as well.

    Thanks for the replies guys
     
  9. bundick

    Active Member

    Dec 19, 2007
    97
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    Loss? There's no loss. Nothing is transferred from the Magnet to the nail.
    Read up on magnets and eventually you'll see the photo of the Iron filings forming on the lines of Flux.
    Those lines are also drawing the molecules in the Nail into alignment.
    There's no loss of energy from the magnet. You could stick a whole box of nails to that magnet and those lines would all still be there.
    They would distort a little to include the lump of nails, but the same number of lines will always exist as long as the magnets properties stay the same.

    Did I get it right?:)
     
  10. mentaaal

    Thread Starter Senior Member

    Oct 17, 2005
    451
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    but then by that definition where did the nail get it's energy from to rise up and stick to the magnet? By the laws of physics, energy is required for movement to occur and the only thing which could conceivably supply this energy has to come from the magnet. So as this energy gets transferred to the nail (firstly as kinetic energy then as potential energy depending on the time you want to look at it) this energy has to get lost from the magnet as energy has to always be conserved. My question is, what does this energy loss do to the magnet? And what effect does the amount of this energy have on the magnet? Is the amount of (i don't even know what to call this energy but i will call it magnetic energy?) this magnetic energy have on the magnet? the more of this energy the magnet has the stronger the magnet? Judging by the complexity of the text i was linked to by one of the replies i would hazard a guess and say that the answer to this question is not easily answered!
     
  11. Salgat

    Active Member

    Dec 23, 2006
    215
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    The more I think about it, the less I think that any energy is lost from magnets, I suppose you could compare them to a spring or to gravity.
     
  12. bundick

    Active Member

    Dec 19, 2007
    97
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    Interesting question. I finally figured out what you were asking. I dont know what the energy is called. Attraction?
     
  13. mentaaal

    Thread Starter Senior Member

    Oct 17, 2005
    451
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    But then where does the nail get the energy to overcome the force of attraction of gravity? everything has potential energy due to gravity and as the nail is raised up its potential energy is increased. This means that it has to have gotten energy from something else. This also means that the "something else" must have lost energy. What else could have lost energy here besides the magnet? Am i correct in my line of thinking? Please, if someone knows better please correct me. Energy transfer has always been a tough cookie for me to crack
     
  14. recca02

    Senior Member

    Apr 2, 2007
    1,211
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    for this to happen the magnet has to at some hight, right?
    so was the magnet in air from the beginning? or was it brought there? was the nail there when it was brought there? or was the nail brought after?
    think now u'll find the answer yourself.

    if the nail was brought there afterwards...the phenomenon which brought it there did the work.
    if magnet was raised near the magnet ...the phenomenon raising the magnet did the work.

    before all of this lets say everything was at its equilibrium position..a state of min Potential energy.... later whichever force made the nail or magnet do work to restore equilibrium and maintain a state of lower PE had to do that much work(at least) to raise the PE of the configuration.
     
  15. mentaaal

    Thread Starter Senior Member

    Oct 17, 2005
    451
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    I was kind of thinking of that as well but lets say that the magnet is suspended by a piece of string tight to a pole or whatever. And the nail was moved horizontally along the ground until it came into range of the magnet to attract the nail. Then what?
     
  16. recca02

    Senior Member

    Apr 2, 2007
    1,211
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    you don't even need to bring the nail in that case..the nail will automatically be pulled to that point since the nail is attracted by the magnet.the magnet hence was at higher PE initially.
    but this is exactly what is your question right? which agency did the work of bringing nail to that PE initially?
    the answer might be the matter/substance evolved in due course of time as magnet and this process gave it the energy to create a magnetic field perhaps...this will require to delve into how a magnetic property actually relates to a matter..is it an intrinsic property etc..
     
  17. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    mentaaal ,

    Be very scared of Maxwell's equations! I was in an EM physics course this year, but I had dropped out because I was taking 8 courses at once. All of the engineers struggled with that class! I'm looking forward to it next september :(

    Steve
     
  18. mentaaal

    Thread Starter Senior Member

    Oct 17, 2005
    451
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    Ok thanks alot for the replies guys. And yes, eeep!
     
  19. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    144
    Although complex, understanding the fundamentals of Maxwell's Equations are not all that bad if you do some background work on the underlying mathematics (easy for me to say I hear you say!). For Faraday's and Ampere's Laws you need a grasp of how the Curl works and understand the interrelation of the electric and magnetic fields, namely a time-varying electric-field gives rise to a time-varying magnetic-field and how a time-varying magnetic-field gives rise to a time-varying electric-field. You should also be clear on the concepts of permittivity and permeability and there influence in the resulting EM waves.

    Couple Faraday's and Ampere's Law (using substitution) and you have the wave equations for the plane wave solutions to the electric and magnetic fields. With the boundary conditions you now have all the fundamental tools for describing the complete interaction of EM waves within an environment.

    Gauss's Laws are based around the divergence operator.

    Maxwell's Equations become considerably more complicated when we start looking at practically applying them; thats where you need to concentrate in your EM Physics courses ;)

    Dave
     
  20. BlueDevry

    Member

    Dec 26, 2007
    22
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    Not really good at physics but my conjecture is that the energy may have more to do with the magnetic properties of the atoms in the objects and the distance that those objects are from each other. The nail gets its potential energy from the fact that opposite polarities attract. This potential energy depends on the strength of the flux and the distance of the objects.
     
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