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A magnetic dipole is the limit of either a closed loop of electric current or a pair of poles as the dimensions of the source are reduced to zero while keeping the magnetic moment constant. It is a magnetic analogue of the electric dipole, but the analogy is not complete. In particular, a magnetic monopole, the magnetic analogue of an electric charge, has never been observed. Moreover, one form of magnetic dipole moment is associated with a fundamental quantum property—the spin of elementary particles. The magnetic field around any magnetic source looks increasingly like the field of a magnetic dipole as the distance from the source increases. == External magnetic field produced by a magnetic dipole moment == In classical physics, the magnetic field of a dipole is calculated as the limit of either a current loop or a pair of charges as the source shrinks to a point while keeping the magnetic moment constant. For the current loop, this limit is most easily derived for the vector potential. Outside of the source region, this potential is (in SI units) : The magnetic field is symmetric under rotations about the axis of the magnetic moment. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Magnetic dipole」の詳細全文を読む スポンサード リンク
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