A magnetic field is always associated with charges in motion. Therefore, the magnetic units can be derived from the current that produces the field. The current in a conductor and its magnetic flux thorough the medium outside the conductor are related as follows.
- The current I supplies a magnetizing force, or magneto-motive force (mmf), that increases with the amount of I.
- The mmf results in a magnetic field intensity H that decrease with the length of conductor, as the field is less concentrated with more length.
- The field intensity H produces a flux density B that increases with the permeability of the medium.