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I Rutherford's model

  1. Apr 24, 2016 #1
    Last edited by a moderator: Apr 25, 2016
  2. jcsd
  3. Apr 24, 2016 #2
    Electrons circling in a wire don't radiate, as OP says. Rutherford atomic model had an electron circling the proton - not in a wire, but held in orbit by attraction of charges. This model was "rejected by physicists" as debajyoti datta says. Partly because it should radiate, lose energy, and dive into the proton, in about 10^-8 seconds. So debajyoti datta wonders why this conclusion holds in the atom model case when it doesn't hold in the wire case.

    There are (I think) a number of possible answers, here's one. The Rutherford model has only one electron (obviously I'm talking of Hydrogen). So, in terms of tech99's answer, we don't have a static electric field pointing radially outwards everywhere, rather it only exists where the electron is at the current point in the orbit (in Rutherford incorrect model). So lines of electric field force are constantly changing direction and must radiate.
     
  4. Apr 24, 2016 #3
    First of all,thanks for picking up my doubt. I would add a little more doubt(s). We all know that accelerating charge produces transient radiation in the form of pulse and time varying current produces steady state harmonic variation radiation. these 2 forms viz.time varying current and accelerating charge are equivalent mathematically. I do not know LaTex,otherwise i would have written the mathematical relation. Now my doubt was, the electron circulates in a wire it's direction of velocity is constantly changing, owing to the fact that it experiences centripetal acceleration. But the acceleration vector and velocity vector are perpendicular to each other, I think that's why it does not radiate. Had there been any non 90 degree angle between acceleration vector and velocity vector then we could have got a transient radiation. Correct me please if I am wrong.
     
  5. Apr 24, 2016 #4
    debajyoti datta: you, tech99, Vanadium 50, and most others at PF I suppose, know more about it than I do. Nevertheless I can give you some great advice! Read http://www.mathpages.com/home/kmath528/kmath528.htm

    When done with that click the link at bottom ("Return to MathPages Main Menu") and read everything else Kevin Brown wrote. Finally: save that link and return to it often.
     
  6. Apr 24, 2016 #5
    I am just a learner, a newborn baby in terms of knowledge, how dare you compare me to others ? .....ha ha....but I am insanely curious. I've printed the page and bookmarked the link for future readings. Thanks for the link.
     
  7. Apr 25, 2016 #6

    tech99

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    Within a metal, we have a great number of free electrons, and they behave like a plasma and have a strong static field pointing everywhere out of the wire. Of course, we do not measure a static field from the wire because the field of the electrons is cancelled by the positive nuclei. But it is still there. And when an accelerating force is applied, the electrons are light and move but the nuclei are heavy and almost do not. So the new component of field, the transverse electric field associated with radiation, is not cancelled by the nuclei and we can observe it.
     
  8. Apr 25, 2016 #7
    Couldn't this be settled by experiment??
     
  9. Apr 25, 2016 #8

    sophiecentaur

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    Wire loop antennae work very well.
     
  10. Apr 25, 2016 #9
    Exactly, so it DOES radiate.
     
  11. Apr 25, 2016 #10

    sophiecentaur

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    Yes, it radiates at the appropriate frequency and not at optical frequencies, as in the inner orbitals of an H atom. QM is the clue here.
     
  12. Apr 25, 2016 #11

    jtbell

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    A loop antenna is driven by an alternating current, in which the electrons' average speed changes back and forth. A wire loop with a constant direct current, in which the electrons' average speed is constant, does not radiate.
     
  13. Apr 25, 2016 #12

    sophiecentaur

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    When DC passes round a loop, the current in every direction is equal so any radiated fields from individual electrons will cancel with all the rest.
     
  14. Apr 25, 2016 #13

    jtbell

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    My memory could be playing tricks on me, but I seem to remember once seeing a derivation for the classical radiation produced by N charges moving at constant speed around a circular path, equally spaced. As N increases, the amplitude of the radiation decreases.
     
    Last edited: Apr 25, 2016
  15. Apr 25, 2016 #14
    That's exactly why I sent you to Kevin Brown. If you were just a student trying to pass a course I wouldn't recommend him - too distracting, and iconoclastic.

    KB is (was?) a smart and knowledgeable guy, with (at least) a PhD and plenty of teaching experience, who thought deeply about physics (and other) issues and tells it like he sees it. Goes along with the establishment view only when it makes sense (which, of course, it usually does). Has a nose for interesting questions, writes good and short essays. As far as I know, he gave up around 1994. I picture him hiding out in a log cabin in Montana, disgusted with modern physics, the whole modern world; but have no idea if that's true. If I were more ambitious, I'd copy his website and be ready to mirror it when it disappears (assuming he didn't object).

    Undoubtedly right, especially for a brief answer (the best kind), but there are also plenty of interesting details I think

    Interesting detail
     
  16. Apr 25, 2016 #15
    So remove the positive lattice ie electrons in a constant current circle ... radiate or not?
     
  17. Apr 25, 2016 #16
    How would you get the electrons to cooperate? Answer may depend on that detail. Also, how closely spaced they are (as jtbell indicates); and how closely you look for the radiation

    By the way, are you aware that a recent study shows that questioning fine points can be bad for your health? Evidently it causes a decrease in financial status leading to physical health issues. Just thought I'd let you know
     
    Last edited: Apr 25, 2016
  18. Apr 25, 2016 #17
    I wouldn't ask then nicely. ....big magnetic field.

    They'll go round.

    too late on that other issue.
     
  19. Apr 25, 2016 #18
    Good spelling, on the other hand, never hurt anybody
     
  20. Apr 25, 2016 #19

    jtbell

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    Now that I've had a couple of cups of coffee, I think my memory must indeed be playing tricks on me. Synchrotron radiation is a fact of life at circular particle accelerators, especially with electrons, and they don't work by sending individual electrons around one at a time!

    I think a more relevant factor for the DC-current-carrying loop is the electron drift speed that corresponds to the current. This is typically on the order of millimeters per second, producing a correspondingly small centripetal acceleration (depending of course on the radius of the loop). And the radiated power varies as the cube of the acceleration IIRC.
     
  21. Apr 25, 2016 #20
    I know LHC sends protons around in packets; guess they're all that way? So the leading and trailing edges of those packets would still have changing fields, producing the synchrotron (what a cool word!) radiation. The dense part of the packet may emit no radiation, in line with sophiecentaur's comment.

    Nevertheless I wouldn't be surprised if you can have (essentially) continuous flow and still get radiation with the right conditions (as houlahound wonders). Perhaps, higher speed combined with tighter loop, for greater centripetal acceleration? However in chip design if the corner of a CPU's bus (for instance) isn't rounded off, the electrons will tunnel through and fly away - so that's pretty extreme acceleration. Yet I don't think they have a problem with radiation emission.

    It seems to me electromagnetism is still not well understood by those who understand it.

    It's amazing that some physicists can tell you exactly how many child universe generations are necessary to produce intelligent life, assuming they reside on 10-dimensional multi-trillion light-year colliding branes (although it's still unknown for 11-dimensional branes, and a massive infusion of taxpayer's money is necessary to research the question). But they can't tell you how a D-cell battery works.

    {EDIT] I'm not thinking of anyone posting at PF! Incredibly brilliant genius can't be bothered with such mundane activity
     
    Last edited: Apr 25, 2016
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