Question

The value of relative magnetic permeability $({\mu }_r$) for ferromagnetic materials is

• A. $({\mu }_r=1$)
• B. $({\mu }_r>>1$)
• C. $({\mu }_r<1$)
• D. $({\mu }_r>1$)

Answer 1

Answer: (B)

$({\mu }_r>>1$)

In electromagnetism, 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.
Ferromagnetic materials exhibit a long-range ordering phenomenon at the atomic level which causes the unpaired electron spins to line up parallel with each other in a region called a domain.
Within the domain, the magnetic field is intense, but in a bulk sample the material will usually be unmagnetized because the many domains will themselves be randomly oriented with respect to one another.
Ferromagnetism manifests itself in the fact that a small externally
imposed magnetic field, say from a solenoid, can cause the magnetic domains to line up with each other and the material is said to be magnetized. The driving magnetic field will then be increased by a large factor which is usually expressed as a relative permeability for the material.
Thus, relative permeability for ferromagnetic material is very high i.e ${\mu }_r\gg 1$