= Solution
A <Stern-Gerlach experiment> uses a nonuniform <magnetic field> to exert force $F_z\simeq\mu_z\,\partial_zB$ on a magnetic dipole. The two resolved beams reveal discrete projections of <spin>, rather than a continuum of classical dipole orientations. For the ground-state <silver> <chemical atom>, filled shells contribute no net <angular momentum> and the outer $5s$ <electron> has orbital <angular momentum> zero, leaving an effective <spin>-$1/2$ magnetic moment. This provides evidence for the electron's two-valued intrinsic <spin>.
Neutral <silver> <chemical atoms> can pass through the apparatus without the large charge-dependent <Lorentz force> that would deflect and broaden a free-<electron> beam. Neutrality isolates the small magnetic-gradient force far more cleanly. The later parts use an ideal <spin> filter model; a literal free-<electron> apparatus requires additional control of charge forces.
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