Electrical Engineering ⇒ Topic : Relation Between B and H

Relation Between B and H

The flux density B produced in a material is directly proportional to the applied magnetising force H. In other words, the greater the magnetising force, the greater is the flux density and viceversa i.e.

The ratio B/H in a material is always constant and is equal to the absolute permeability (μ = μ₀ μ_r) of the material. This relation gives yet another definition of absolute permeability of a material.

Suppose a magnetising force H produces a flux density B_o in air. Clearly, B_o= μ₀H . If air is replaced by some other material (relative permeability μ_r and the same magnetising force H is

Hence relative permeability of a material is equal to the ratio of flux density produced in that material to the flux density produced in air by the same magnetising force.

Thus when we say that μ_r, of soft iron is 8000, it means that for the same magnetising force, flux density in soft iron will be 8000 times its value in air. In other words, for the same crosssectional area and H, the magnetic lines of force will be 8000 times greater in soft iron than in air