19. If an electron travels with speed v around a circle of radius r, then the magnitude of the orbital magnetic dipole moment is: (A)evr/2 (B)ev/r (C)ev/2πr (D)2πer/v (E)2πev/r

5. A solid wheel with mass M, radius R, and rotational inertia MR²/2, rolls without sliding on a horizontal surface. A horizontal force F is applied to the axle and the center of mass has an acceleration a. The magnitudes of the applied force F and the frictional force f of the surface, respectively, are: (A)F = Ma, f = 0 (B)F = Ma, f = Ma/2 (C)F = 2Ma, f = Ma (D)F = 2Ma, f = Ma/2 (E)F = 3Ma/2, f = Ma/2

19. If an electron travels with speed v around a circle of radius r, then the magnitude of the orbital magnetic dipole moment is:
(A)evr/2
(B)ev/r
(C)ev/2πr
(D)2πer/v
(E)2πev/r

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