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Reality_Patrol
#9
Oct12-04, 11:25 AM
P: 111
Quote Quote by zefram_c
Reality_Patrol: You seem to have a number of misconceptions; let me try to clear those up.
Yes I do, thank you.
Quote Quote by zefram_c
-The gyromagnetic ratio is the ratio of the measured magnetic moment to the angular momentum (here: spin) of the object in question.
Got it - so any particle with a magnetic moment (charged or not) can have one.
Quote Quote by zefram_c
-In classical QM, this ratio is uniquely determined from the charge and mass of the particle. However, for electrons and other elementary particles (protons and neutrons do NOT qualify as such), the observed result is slightly over twice the classical result.
-The Dirac theory accounts for the factor of two and attributes it to the relativistic wave equation that electrons satisfy.
OK, thanks, but is the factor of (2) just an artifact of the mathematical formalism, or does/can it be given some intuitive physical interpretation?
Quote Quote by zefram_c
-The slight correction (called the anomaly) is accounted by quantum electrodynamics through the interaction of the electron with the background EM field.
Ahh, here's where I'm really weak. I probably just need to study up on QED - though that's NOT very appealing.
Quote Quote by zefram_c
-Electric charge is the fundamental property, not magnetism. Neutrons can have a magnetic moment because they are composed of charged constituents (quarks).
Yes, of course that's the standard explanation. My personal research involves looking into the possibility that magnetism is fundamental. By this I don't mean magnetic monopoles, I accept the evidence against their existence. I mean the obvious: the fundamental magnetic charge sources a magnetic field in a dipole configuration. I've never seen anything on this possibility. A corollary I also plan to investigate is: a magnetic charge in motion (spinning) appears to be an electrical charge to a stationary (non-spinning) observer! All of this is pure conjecture on my part, and most likely wrong - but fun to look into!
Quote Quote by zefram_c
-A first-order calculation for proton/neutron magnetic moments based on the quark model can be found in "Introduction to Elementary Particles" by D. Griffiths, p180-182.
Thanks for the reference, I'll look into getting it. I'd prefer an on-line version that's free of course!