試題詳解

16. Two short uniform cylindrical-shaped magnetic bars, with identical length L and radius R, are lined up through their cylindrical axis and separated by a distance x with respect to the center of mass of each one. Considering the pure dipole approximation, x>>L> R, the magnetic force between two magnetic dipoles are proportional to the p-th power of the distance x. What is the value of p?
(A)-2
(B) -3
(C) -4
(D)-5
(E) -6