For a bar magnet, this would be the number of field lines emanating from the north pole. For an electromagnet, it would be the number of lines emanating from the north end of the core. Basically, these are the same, only the north pole of an electromagnet is determined by the direction of current flow. When a current-carrying conductor is looped around a cylindrical core, the magnetic field lines around the conductor concentrate in the center of the core, and a magnetic field is created such that its strength H is equal to the ratio of the product of the current and the number of turns, or loops, to the length of the core. Another parameter of magnetism is magnetic flux density B .
Flux density is the ratio of flux to the area through which the flux passes.
The magnetic permeability of a material represents the degree to which it can concentrate magnetic field lines. The more concentrated the field lines, the greater the magnetic permeability. Magnetic permeability is the ratio of flux density to field strength. 50.265 Oe, the flux density of an air core would be The permeability of materials is often given as relative permeability . This is the ratio of the material's absolute permeability to that of air.