Definition: The ability of the material to conduct magnetic lines of force through it is called the magnetic permeability of that material. In other words, it is the capability of the magnetic material to support the development of the magnetic field. The magnetic line of force is directly proportional to the conductivity of the material. Their SI unit is Henry per meter (H/M or Hm2) or newton per ampere square (N-A2).
The greater the magnetic permeability of the material, the greater is its conductivity for the magnetic lines of force and vice versa. The magnetic permeability of the air or vacuum is poorest and is represented as μ0 where μ0 = 4π×17-7 H/m. The magnetic permeability of the material is represented by μ.
The figure above shows that when a soft ring is placed in the magnetic material, most of the magnetic lines will pass through it instead of air as the ring provide the easiest path for them. The permeability of the material is the ratio of the flux density to the applied field density of the magnetic material. It is expressed by the formula given below
Relative Permeability – The absolute or actual permeability mu (μ) of material is much greater than the absolute permeability of air u0. The relative permeability of the magnetic material is given in comparison with air or vacuum.
Hence the relative permeability is defined as the ratio of the permeability of material μ to the permeability of air or vacuum u0 is called the relative permeability ur of the material.
The above relation shows that a field intensity H produces a flux density B0 in air, whereas the same field intensity produces a flux density B when the air is replaced by some magnetic material. This gives another definition
The relative permeability of the air would be u0/u0 = 1.The value of the relative permeability of all the non-magnetic material is also 1. Their value is as high as 8000 for soft iron, whereas, its value for permeable is as high as 5000.