A property of magnets, currents circulating in loops, and spinning charged particles that dictates the strength of the turning force exerted on the system by a magnetic field, B; symbol µ, units A.m2 (amp.metre-squared) or J/T (joules per tesla); a vector quantity; also called the magnetic dipole moment. Turning force (torque), ?, is ? = µBsin?, where ? is the angle between µ and B directions.
Spinning charged particles such as electrons and protons behave like minute current-carrying coils, and so have magnetic moments. Neutrons, despite having zero net charge, also have a magnetic moment, since they spin and are composed of charged particles; their magnetic moment is exploited in neutron diffraction experiments. Atomic nuclei have magnetic moments which are exploited in nuclear magnetic resonance. For certain atoms, the magnetic moment contributions from various electrons, either from their spins or motion about the atomic nucleus, do not cancel. Such atoms have large net atomic magnetic moments, which form the basis of magnetic properties of bulk materials such as paramagnetism and ferromagnetism.
For a magnet in a magnetic field, a force acts that tries to align its poles in the direction of the field (which is how a compass works). Spinning particles precess in a magnetic field, ie the direction of their spins (hence magnetic moments) rotates about the field direction. The magnetic moment of the electron (9·285 × 10?24 J/T) is due solely to the fact that the electron is a spinning charge. For comparison, this is equivalent to a current loop the size of an atomic nucleus carrying a current of 300 000 A. The magnetic moment of a single loop of radius 1 cm carrying a current of 1 A is 3 × 10?4 J/T.
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In physics, the magnetic moment or magnetic dipole moment is a measure of the strength of a magnetic source.
The magnetic moment in a magnetic field is a measure of the magnetic flux set up by the gyration of an electric charge in a magnetic field.
Explanation
Magnetic moment can be explained by a bar magnet which has magnetic poles of equal magnitude but opposite polarity.
The equation for magnetic moment in the current-carrying loop, carrying current I and of area vector a for which the magnitude is given by:
μ = Iawhere
μ is the magnetic moment, a vector measured in ampere–square metres, or equivalently joules per tesla, I is the current, a scalar measured in amperes, and a is the loop area vector , having as x, y, and z coordinates the area in square metres of the projection of the loop into the yz-, zx-, and xy-planes.Magnetic moment in a magnetic field
The magnetic moment of an object is a vector relating the aligning torque in a magnetic field experienced by the object to the field vector itself. The relationship is given by:
τ = μ × Bwhere
τ is the torque, measured in newton-metres, μ is the magnetic moment, measured in ampere-square metres, and B is the magnetic field, measured in newtons per (ampere-metre).The alignment of the magnetic moment with the field creates a difference in potential energy U:
U = −μ ∙ BMagnetic moment of electrons
Electrons and many nuclei also have intrinsic magnetic moments, an explanation of which requires a quantum mechanical treatment and relates to the intrinsic angular momentum of the particles as discussed in the article electron magnetic dipole moment.
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