The answer I'm hoping to achieve from this discussion is how high a field applied to air has to be in order for it's magnetic flux to match the magnetic flux of a ferrous material. As you may know, ferrous materials are used as magnetic cores, but once the applied field reaches a certain value, the magnetic flux inside that ferrous material becomes saturated and no longer increases. However, no matter how high a field is applied to air, it always increases linearly (not positive about this). Here's a graph of what I'm trying to illustrate: http://upload.wikimedia.org/wikipedia/commons/thumb/0/04/Permeability_by_Zureks.svg/500px-Permeability_by_Zureks.svg.png If you notice in the graph, uf(ferrous permeability) starts to level out at a certain H value. However, u0(permeability of air) continues to increase linearly. Can anyone help me find the H value where air and ferrous materials meet?