Permeability

Let us consider a coil having air as the medium. When the alternating current supply is given to the coil, then it set up a certain flux. If now a same coil is wound over a magnetic material, then the amount of flux generated by the coil increases for the same current. Hence it is observer that the introduction of magnetic material, increased the flux density in the magnetic circuit or a coil. Hence for given nagnetising force, the measure of effectiveness of increasing flux density in a magnetic medium depends on the material and the property is called permeability of the material. The unit of permeability is Henry / meter. Permeability of the material is given by

Permeability is directly proportional to the Magnetic flux density and inversely proportional to the magnetic field strength.

Relative Permeability

Relative permeability is the ratio of magnetic material and the permeability of air.