Question

Permeability U of a ferromagnetic substance

Answer 1

Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. Hence, it is the degree of magnetization that a material obtains in response to an applied magnetic field.

In electromagnetism, the auxillary magnetic field  H represents how a magnetic field B influences the organization of magnetic dipoles in a given medium, including dipole migration and magnetic dipole reorientation. Its relation to permeability is



where the permeability, µ, is a scalar if the medium is isotropic or a second rank tensor for an anisotropic medium.

A ferromagnetic material, such as iron, does not have a constant relative permeability. As the magnetizing field increases, the relative permeability increases, reaches a maximum, and then decreases. 

In ferromagnetic materials, the relationship between B and H exhibits both non-linearity and hysteresis: B is not a single-valued function of H, but depends also on the history of the material. For these materials it is sometimes useful to consider the incremental permeability defined as

Answer 2

Permeability of a ferromagnetic substance is greater than greater than 1