3. Permeability(磁导率) Take the long solenoid(长直螺线管) as an example: (●● 0 .Ooooooo.o°10o° P B 888X88888888⑧8888888888 The ratio of B and Bo is called the relative permeability of the material and represented by u B3. Permeability（磁导率） • P  B0  0 I • P  B  0 I Take the long solenoid(长直螺线管） as an example: The ratio of B and B0 is called the relative permeability of the material and represented by :  r  = B B  r