are counter-rotating magnets DANGEROUS?

Discussion in 'General Science & Technology' started by IamI, Sep 6, 2007.

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  1. kevinalm Registered Senior Member

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    Yeah, you are pretty much limited to power line frequencies, maybe up into the audio band. And since one of the 'other' limitations I mentioned includes that the physical dimensions of the emitter need to be at least of the same order of size as the wavelength of the e/m wave for efficeint wave formation, you're pretty well sunk.
     
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  3. Read-Only Valued Senior Member

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    Agreed. And allow me to modify that last statement to read: "Metakron's idea is pretty well sunk."

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  5. MetaKron Registered Senior Member

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    That's putting words in my mouth. When you have two magnets near each other and one or more is spinning, what you may potentially get as radiation is nearly a total mystery to me. I won't make any serious statements about that, two magnetics parallel to each other, one or more spinning, without looking it up or experimenting. The interactions between field lines not only would be interesting, they might settle a question or two about magnets.

    You don't seem to know much about electromagnetism, seriously. All that is needed for electromagnetic radiation is a changing magnetic field and everything else is a technicality. It wouldn't be all that difficult to produce a sine wave of over 100 Hz and the limitation is obviously how fast you can spin the magnet. The magnet can be spinning or vibrating. Schemes can be made to shake the magnet back and forth at frequencies up to several thousand hertz can be created.

    It doesn't matter to the detector if the detector is moving or the magnet is moving or both. It will still detect a changing magnetic field. This is first year physics.

    (edit) When you have two counter-rotating magnets their field lines cut each other an unknown but large number of times.
     
    Last edited: Sep 7, 2007
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  7. MetaKron Registered Senior Member

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    Incorrect. As I already said, permanent magnets are magnets because more of its electrons orbit in one given plane than the rest. That is the electrical component. The "pure" magnetic field is much larger than the electron orbits that generate it, or the mass that contains those electrons, but it also still has an electrical component at right angles to the magnetic component. The relationship is reflexive. A magnetic field is generated by a moving electrical charge and the magnetic force lines have an electrical charge to them. "Out there" it is a static electrical charge.
     
  8. spidergoat Valued Senior Member

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    It really depends on how powerful the magnet is. I have seen some electromagnets that weigh more than a small car and need to be water cooled.
     
  9. James R Just this guy, you know? Staff Member

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    Read-Only:

    I think you're getting sidetracked here.

    If we're talking about electromagnetic waves, you agree that EM waves can travel in vacuum. Right?

    And what are EM waves? They are self-propagating electric and magnetic fields. Now, tell me your theory on HOW those fields self-propagate, without wires or conductors anywhere near.

    Faraday's law can be formulated to discuss the induced EMF around a loop in space when the magnetic flux through that loop changes. This effect occurs whether the loop is an actual conducting loop, or just an imaginary loop in space. If you happen to place a conductor on the loop, the induced EMF will produce an induced electric current. You seem to recognise that currents can be produced, but you've missed the main game, which is that an electric field is produced, regardless of the presence or absence of any conductor. It is that field which produces the current you mention when there happens to be a conductor in place.

    I'd have to think that one through. What produces EM radiation is accelerating charge. Charge moving at constant speed only produces a static magnetic field.

    So, a magnet moving at constant velocity may not produce EM radiation, as you say. I'm not 100% sure. Accelerating the magnet certainly would, though.

    But you've changed the situation here. The original question asked about a rotating magnet, not one moving in a straight line at constant speed.
     
  10. James R Just this guy, you know? Staff Member

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    MetaKron:

    If you take an ordinary bar magnet which is stationary, there will be essentially zero electric field outside that magnet, and a definite magnetic field. Do you agree?
     
  11. MetaKron Registered Senior Member

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    No, because you said electric field, not electric current. You have an essentially static magnetic field, so the electrical field at right angles to it is essentially static on the macro scale.

    Thinking about it this way, it's not just because there is a current through a wire that there is a magnetic field. It is also because the electrical charges moving through the wire are aligned with each other.

    http://en.wikipedia.org/wiki/Magnetic_field

    I will consider Einstein's theory to be adequate for this purpose for the time being.
     
  12. James R Just this guy, you know? Staff Member

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    I am claiming that, outside a stationary standard bar magnet, there is no electric field. Do you agree or disagree?
     
  13. MetaKron Registered Senior Member

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    Disagree.
     
  14. James R Just this guy, you know? Staff Member

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    Ok, MetaKron.

    Please describe for me how the net electric field in the space surrounding a standard, stationary, bar magnet, is produced.
     
  15. MetaKron Registered Senior Member

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    5,502
    God makes it.

    I already gave you a link that mentioned what Einstein proved about that. If you're not happy with that, go fish.
     
  16. James R Just this guy, you know? Staff Member

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    MetaKron:

    I don't think you understand what your link about Einstein's relativity does and does not support.

    Your refusal to discuss the matter just provides evidence of your shaky grasp of the relevant concepts.

    I think we're done, then.
     
  17. MetaKron Registered Senior Member

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    You don't seem to know the basic theory and don't seem to want to learn. Yep, we're done.
     
  18. James R Just this guy, you know? Staff Member

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    You can't even explain this "basic theory" in your own words, MetaKron.
     
  19. MetaKron Registered Senior Member

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    No, it does not take current flowing in a conductor to create EM radiation. The magnet can be moved back and forth. It's pretty easy these days to mount a strong permanent magnet on a vibrating diaphragm. Some of the supermagnets that you can get these days are extremely small, smaller than a BB shot. You can also mount the magnet on a spinning disk.
     
  20. kentpollard Registered Member

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    still curious about rotating magnets

    I was fiddling with magnetic coupling on the gas turbine (90Krpm), and I was thinking the NIB magnets spinning perpendicular to their poles would really be a 1,500 HZ EM field of some sort (E because the magnet moves and M because it doesn't move fast enough). In fact just eyeballing it the M component looks like the M component of a 1.5KHZ radio wave (in the ULF band).

    Wikipedia claims the ULF band is used for communication in mines, which implies to me that it's fairly short range but penetrates rock well.

    Does anyone really have a clear idea of what spinning the magnets could do, EM wise?

    The magnets are the japanese type: put them under a plate with water in it and they'll make a dimple in the water. They're pretty strong.

    Also, I realized late in my ruminations that I had simplifyingly assumed that there was a single magnet centered, but in fact there are four offset from the axis.
     
  21. DRZion Theoretical Experimentalist Valued Senior Member

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    I've had 2 meal cards destroyed due to magnets, they are more dangerous than you think! Especially if you are hungry!!
     
  22. bakakun346987469873 Registered Member

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    Since no one answered your question I will

    There is a danger. The specificity of why is arbitrary to the question. If you plan on playing with this be careful of microwave especially, or if you are near an airport. Think of the electromagnetic spectrum as the waves they are. Using to magnetic fields with energy input will cause varying oscillation of wave and function of the wave.

    Its like how a musical instrument can alter sound waves.

    Fin
     
  23. siledre Registered Senior Member

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    they're only dangerous if they become a counter-rotating magnet golem, then you better run. throw your atm cards at them, it slows them down. credit cards anger them though.
     
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