• The elements lie in d-block or f-block of periodic table and they have large number of unpaired electron which contribute to spin dipole moment so they have large dipole moment and are strongly magnetized.
  • Example:- Fe, Co, Ni, Gd, Dy
  • Since ferromagnetic material is a strongly magnetized the magnetic field line converge when they passed through ferromagnetic material.
  • When magnetic field is removed the dipoles remain align inside the material giving rise to residual flux density.

Residual flux density (Br)

  • Virginal curve is the magnetization curve of freshly prepared material.
  • Coercive force (Hc) :- It is the value magnetic fields that needs to be applied to make flux density zero.

Domain theory

  • An iron piece normally does not exhibit magnetism unless it is magnetized which means net dipole moment in absence of magnetic field should be zero but ferromagnetic material must have residual magnetism and to explain this discrepancy we study domain theory.
  • After removal of magnetic field the dipole inside each domain remain aligned. But the domain are not aligned with each other.


  • It is the phenomenon in which dimension of a ferromagnetic material changes when magnetic field is applied.
  • If alternating magnetic field is applied then material expands and compresses in alternate half cycle by which mechanical vibrations are produced which are observed as a humming sound in a transformer.
  • To damp out mechanical vibration transformer should be mounted on mud/ soil or a rubber mat.


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