When a spin possessing particle is in magnetic field B the spin 'rotates' around B. By example electron with spin on X will rotate perpendicular to B. But is this real? Can it be observed? Does this precession change the current in the coil creating B?
Secondly I tried to find out something about the classical situation. E.g. a compass must classically rotate then around B even when its blades are perpendicular to B. But than I could not find anything. Also it will look like perpetum mobile.
Thirdly I didn't see or can read about small magnets precessing around B? The spins must look like small magnets but there is nothing to confirm this?? And less about their effect on the B? Do really small magnet move precessingly around B and does this show up on the current of the coil?
You will be interested in the following page on Needle Magnetometer, http://physics.aps.org/articles/v9/53
Thank you Kiyoshi! I see that at least they had the same questions. But it would be hard to get their article.
Dear dr. Ilian Peruhov,
about your first question, Robert Pohl (https://en.wikipedia.org/wiki/Robert_Pohl) devised a a working mechanical analogy between a sprinkler and spin transitions, which he included in the 1975 German edition of his book “Elektrizitätslehre”. I attach the pages I refer to. Abb. 14.14 shows the device on which the analogy is based. However, this mechanical analogy is not shown in every edition of Pohl's book.
While Larmor precession is a classical explanation of why matter shows a magnetic moment when in a magnetostatic field, NMR is a way of measuring the free induction decay (FID) response of diamagnetic substances (in solution). Whatever explanation is given for diamagnetism, the main problem when trying to visualize Larmor's precession of spin is that the spin itself is not a classically visualizable property. Thus, I would say that the directly observed quantity is the FID, indeed.
As for the directivity of magnetized needles, that remarkable property belongs to a small class of substances. The majority of matter is only slightly affected by magnetic fields, and one needs strong fields to observe tiny effects. Finally, you should keep in mind that, although NMR instruments have a spot where the field is homogeneous, generally strong magnetic fields are a bit non-homogeneous.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Electromagnetism