Phenomenological Description of Magnetic Behavior

instead of a straight wire segment, a current-carrying loop is placed in the magnetic field, a torque (turning force) is exerted on the loop. The torque, t, is given by  

Any dipolar magnetic field pattern is symmetric with respect to rotations around a particular axis. Hence, it is customary to describe the magnetic dipole moment that creates such a field as a vector with a direction along that axis. The SI units of magnetic moments are thus A m. From Eq. 8.2, the torque experienced by the magnetic moment in the external field is given by the cross product of the magnetic moment and 

A macroscopic sample (which need not be a bar magnet or current-carrying coil), comprised of a very large number of microscopic (atomic) magnetic moments, can be defined as the magnetization, M, as the net magnetic moment per unit volume (SI units A/m, gauss/cm, or emu/cm in the cgs system)  

- is the concentration of atomic moments, The magnetization and the magnetic flux density (also called the induction) ate related to the magnetic field intensity H within the sample, via the equation  

The magnetization is often hnearly proportional to the internal held strength, the constant of proportionahty being the magnetic susceptibility, x- 

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