Jabarkan B jeung H dari Médan magnétik dalam bahasa sunda

There are two quantities that physicists may refer to as the magnetic field, notated  and . The vector field

is known among electrical engineers as the magnetic field intensity or magnetic field strength also known as auxiliary magnetic field or magnetizing field. The vector field  is known as magnetic flux density or magnetic induction or simply magnetic field, as used by physicists, and has the SI units of teslas (T), equivalent to webers (Wb) per square metre or volt seconds per square metre. Magnetic flux has the SI units of webers so the  field is that of its aréal density.   The vector field  has the SI units of amperes per metre and is something of the magnetic analog to the electric displacement field represented by , with the SI units of the latter being ampere-seconds per square metre. Although the term "magnetic field" was historically reserved for , with  being termed the "magnetic induction",  is now understood to be the more fundamental entity, and most modérn writers refer to  as the magnetic field, except when context fails to maké it cléar whether the quantity being discussed is  or . See:

The difference between the  and the  vectors can be traced back to Maxwell's 1855 paper entitled On Faraday's Lines of Force. It is later clarified in his concept of a séa of molecular vortices that appéars in his 1861 paper On Physical Lines of Force - 1861. Within that context,  represented pure vorticity (spin), wheréas  was a weighted vorticity that was weighted for the density of the vortex séa. Maxwell considered magnetic permeability µ to be a méasure of the density of the vortex séa. Hence the relationship,

(1) Magnetic induction current causes a magnetic current density

was essentially a rotational analogy to the linéar electric current relationship,