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Mysteries of a simple spiral (coil).

  1. Jun 4, 2005 #1
    Let we have a piece of wire, copper, for example.
    Let we have the generator of alternating current with changing frequency.
    We connect the ends of a wire to clips of generator of an alternating current and then turn it “ON”.
    Resistance of a piece of wire does not depend on frequency of a current and will be identical on any frequency. This resistance refers to "active" one. It reflects only properties of a material of conductor (specific resistance).
    The same effect will be in a case of any changes of the form of wire in 2d plane.
    But as soon as the form of a piece of wire gets the third dimension , its properties will sharply changed. Resistance of a spiral (coil) becomes dependent from the frequency.
    It grows with increase of frequency. This resistance is named as “inductive resistance” and it does not depend on material of conductor.
    Why?
    Thanks.
     
  2. jcsd
  3. Jun 4, 2005 #2

    ZapperZ

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    This is not correct. A IDEAL inductor will not have any resistance, only a reactance. In that case, the reactance will depend only on the current, the freq., and the inductance. However, a REAL inductor will always have a resistance. This would be the same as putting an ideal inductor and another resistor in SERIES. When you have that, the resistor will change the current that's flowing in the circuit. Thus, the TYPE of material will definitely affect this type of circuit.

    Zz.
     
  4. Jun 4, 2005 #3
    Sorry? We can always make an identical current for various materials.
    Besides that, the super conductor coil made of various materials has no any resistance. My question about the reason of occurrence of inductance.
    Only change of the SPATIAL configuration of conductor leads to radical change of its properties. Is it not so?
     
  5. Jun 5, 2005 #4

    Meir Achuz

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    Even in a straight wire, the resistance will generally increase wilth frequency because at higher frequencies the current density is no longer uniform but gets stronger toward the surface. This is called "skin effect"
    The "self inductance" (I have never seen it called "inductive resistance", which is actually something else.) of the wire will increase as you form a spiral, because the inductance depends on the magnetic linkage between different parts of the wire.
    As different parts of the wire come closer together, the linkage, and therefor the inductances, increases.
     
  6. Jun 5, 2005 #5
    Yes, certainly. «Skin effect» is consequence of that a real wire has an internal volume. However just to say “the inductance depends on the magnetic linkage between different parts of the wire ” is not enough in my opinion.
    If make any flat (2d) figure of a wire such as a sinusoid or a spiral they will not have inductance. Inductance will appear only if these figures are stretched in the third dimension.
    Now we’ll replace a real wire with some ideal channel in which can be distributed only one EM wave. Further we’ll form the same figures of this channel . What can we see in this experiment?
     
  7. Jun 5, 2005 #6

    pervect

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    I don't think there is much mystery here. In order to have current through a conductor, the conductor has to have a cross sectional area. If the conductor is an ideal two dimensional figure, the cross-sectional area is zero, and so is the current.

    This makes both the resistance

    R = V / I

    and the inductance

    L = V / (dI / dt)

    equal to infinity (not zero), as I and dI/dt are both zero. The ulitmate cause is the same, you can't carry any current through a counductor unless it has a cross-sectional area.

    To have current flow through zero area would require an infintie current density, which is unphysical.
     
  8. Jun 6, 2005 #7

    ZapperZ

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    Only if you CHANGE the dimensions of the wire. The resistivity of a length of material depends on a bunch of parameter, not the least of which is the type of material. If you fix the dimensions, then you can't tell me the resistance remains the same if you replace Cu with Pb!

    And once you change the dimensions, then you no longer have the identical inductor.

    And you don't think replacing a Type I superconductor with a Type II superconductor will NOT cause any possible change in the property of that inductor regardless of the induced magnetic field? Or what about the change in the critical current density as you change to different magnetic field? This will certainly affected the induced magnetic field. It isn't this trivial!

    Zz.
     
  9. Jun 6, 2005 #8
    Well, well, well
    I do not doubt that you, guys, perfectly know how this stuff (inductance) works.
    I do not doubt also that you perfectly know how another stuff (mass) works too.
    But I think all of you will be surprised if I’ll be saying that this two stuff have many concurrences in their properties (too much).
    So?
     
  10. Jun 6, 2005 #9

    ZapperZ

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    No, it will not surprise me, because all you have done is to STATE it, and not reason it. It requires no knowledge of anything to state anything. Quacks do this all the time.

    The one thing about may parts of physics that you seem to have forgotten is that one can actually TESTS these things out. I challenge you to find 2 identical inductors with identical dimensions made of widely different materials and try it out (suggestion: Cu and Al2O3). Tell me if they produce the result you described in the very first post of this thread.

    Zz.
     
  11. Jun 9, 2005 #10
    Just add the corresponding resistor to a coil of Cu in series.
    Resistance is the property of material but inductance,as well as mass, is the property of spacetime.


    Michael.

    ------------------------------------
    Ability to surprising is one of the main properties of the person. At donkeys this property is absent completely.
     
  12. Jun 9, 2005 #11

    ZapperZ

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    Which is EXACTLY what I said in my original response. So you have contradicted yourself.

    Are you sure? I thought it was a property of chicken feathers?

    Zz.
     
  13. Jun 12, 2005 #12
    I do not see any contradiction here. An additional resistor only changes resistance of the coil to a direct current, and distinction between these two coils will be shown only at the big current and small frequency. With increase of frequency and reduction of a current the distinction of coils will decrease too. Their resistance to a current of high frequency many times exceeds resistance to a direct current. A value of additional resistor is insignificant in this case.
    Resistance of coil to an alternating current of high frequency depends on its constructive (spatial) parameters only.
    The coil creating resistance to a current of high frequency can be used as a model of occurrence of mass at a wave - particle.
    Is it not the mystery on today?

    MASS (inertia) this resistance to the carrier of force. The carrier of force at subatomic level is the PHOTON (EM-wave).
     
  14. Jun 12, 2005 #13

    ZapperZ

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    Let's examine what you have said, shall we?

    And then, I replied:

    But then, you counter with:

    This makes no sense, and inconsistent with what you are now claiming. Your original argument is that INDEPENDENT of the material being used in the inductor, you will get the SAME "inductive resistance". And now, just to get the same current, you want to CHEAT and add a resistor in series, which was NEVER part of the original scenario.

    This tells me that you're making things up as you go along.

    I would not even comment on the "wave-particle" thingy because this thread is already on the verge of being shoved to where most of your threads have ended up.

    Zz.
     
  15. Jun 12, 2005 #14

    Gokul43201

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    This seems to be the point being made out of all this banter (that there is some special "spacetime" effect that changes things when you go from 2D to 3D - and while this is true of some other phenomena in the solid state, it doesn't apply here ) :

    And that's just plain WRONG. You do have inductance in 2D configurations just as well. Take a wire and make it do a few zig-zags or make a planar spiral. Stick it to a function generator and see what happens.

    If you can not do that, simply download this simulator design a planar inductor and see what happens. If that doesn't do it for you, Google "planar inductor" or "planar spiral inductor". These have been around for about a decade now and are integral components of surface-mount and microchip technologies.

    THERE IS NO MYSTERY HERE.
     
    Last edited: Jun 12, 2005
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