Page 477 - Basic Electrical Engineering

Figure 5.5 (a) Magnetizing force applied to a magnetic material; (b) incomplete B–H curve of two
magnetic materials

5.1.5 Relative Permeability

The permeability of a magnetic material is compared with that of free space
and is called relative permeability. The relative permeability indicates how

many times the material is more permeable than air. Permeability, μ is
expressed as

μ = μ μ (5.5)
r
0
where μ is the permeability of free space and μ is the relative permeability,
o
r
and B is the magnetic flux density.

Magneto motive force (MMF) and magnetic field strength, H

When a current, I flows through a coil of N turns, the MMF, F is the total

current linked with the magnetic circuit, i.e., NI amperes. If the magnetic
circuit is of uniform cross-sectional area, the MMF per unit length of the

magnetic circuit is called magnetic field strength, H.

Thus,