The permeability of a magnetic material describes the ability of that material to contain a magnetic field inside itself (this magnetic field is generated by a current carrying conductor in the presence of the material). Permeability is one of the primary parameters used to select a core material during the magnetic component design procedure. The graph displayed here illustrates the advantage of using a ferromagnetic material over open air as an inductor core. B in the graphs here represents the Tesla, a unit used to quantify the magnetic flux density and therefore the magnetic field size. The Tesla is equal to 1 volt (V) of EMF second(s) per square meter (m^2) – (volt second per square meter)   Formula: 1T=1(V*s/m^2)    H represents the magnetizing force quantified in Ampere turns per meter. The second curve represents the permeability of a core material as the magnetizing force increases. It is apparent that after the permeability reaches its apex, the material becomes less permeable and finally reaches 0 again. At this point the core material is no longer useful to the component and it will respond to the current as an air coil.