What is Magnetic moment?
{{complex|date=September 2023}} {{Electromagnetism|cTopic=[[Magnetostatics]]}} The '''magnetic moment''' of a [[magnet]] is a quantity that determines the [[Force (physics)|force]] that the magnet can exert on electric currents and the [[torque]] that a [[magnetic field]] will exert on it. A loop of [[electric current]], a bar [[magnet]], an [[electron]], a [[molecule]], and a [[planet]] all have magnetic moments. Both the magnetic moment and magnetic field may be considered to be [[vector]]s having a magnitude and direction. The direction of the magnetic moment points from the south to north pole of a magnet. The magnetic field produced by a magnet is proportional to its magnetic moment as well. More precisely, the term ''magnetic moment'' normally refers to a system's '''magnetic dipole moment''', which produces the first term in the [[multipole expansion]] of a general magnetic field. The [[dipole]] component of an object's magnetic field is symmetric about the direction of its magnetic dipole moment, and decreases as the inverse cube of the distance from the object. == Two definitions of moment == In text books, two complementary approaches are used to define magnetic moments. In pre-1930's textbooks, they were defined using magnetic poles.<ref name=Brown62>{{cite book|last=Brown, Jr.|first = William Fuller|author-link = William Fuller Brown, Jr.|title = Magnetostatic Principles in Ferromagnetism|publisher = [[North-Holland]]}}</ref> Most recent textbooks define it in terms of Ampèrian currents. === Magnetic pole definition === [[Image:VFPt dipole electric.svg|thumb|200px|upright|An electrostatic analogue for a magnetic moment: two opposing charges separated by a finite distance.]] Physicists represent sources of magnetic moments in materials as poles. The North and South poles are an analogy to the positive and negative charges in [[electrostatics]]. Consider a bar magnet which has magnetic poles of equal magnitude but opposite [[Polarity (physics)|polarity]]. Each pole is the source of magnetic fo