# proton magnetic moment flip angle 54.7 in an external magnetic field

by mkj
Tags: angle, field, flip, magnetic, magnetic moment, moment, precession, proton
 P: 5 i am reading about MRI. i have seen several in several textbooks that the angle between the direction of the proton magnetic moment μ and the direction of the external magnetic field is 54.7 how did they find that theoretical or experimental if theoretical how can we calculate that
 Sci Advisor HW Helper Thanks PF Gold P: 26,127 hi mkj! loosely speaking, the angular momentum P is fixed if there's no magnetic field, there's no problem … the "spin axis" can be in any direction if there is a magnetic field in the z direction, the component Pz is quantised, and (for a spin-half particle) must be P/√3 so the angle between P and z must be cos-11/√3, = 54.74° (see eg http://www.chem.wisc.edu/areas/reich...hmr-00-nmr.htm)

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