Question

Which of the following refers to the magnetic force required to demagnetize a material?
A) Retentivity
B) Coercivity
C) Energy loss
D) Hysteresis

Answer 1

Hint:Removing the external field usually demagnetizes materials. But in ferromagnetic materials, the magnetization persists upon the removal of the field. This can be viewed as a resistance of the material to demagnetize. Hysteresis is exhibited by these materials. The resistance is essentially a measure of the field intensity required to demagnetize the material.

Complete step by step answer.
Step 1: Explain the nature of the magnetic field force that must be applied to demagnetize the material.
Magnetic materials can be categorized as diamagnetic materials, paramagnetic materials and ferromagnetic materials.
Ferromagnetic materials are substances which get strongly magnetized in the presence of an external field. And if the field is removed, the magnetization in these materials will persist. To completely demagnetize the material the field must be increased in the reverse direction to a particular value. This value of the field intensity is called coercivity.

Therefore, the magnetic field intensity exerted in the reverse direction to demagnetize a ferromagnetic material is called coercivity.

Additional information: Diamagnetic materials tend to repel the magnetic field lines when placed in an external magnetic field. Copper, Lead, Silicon are examples of diamagnetic material.
Paramagnetic materials possess no net magnetization in the absence of the field. But they get weakly magnetized when they are placed in an external magnetic field. If the field is removed the material loses its magnetization.

Note: Ferromagnetic materials get strongly magnetized because, in the absence of a field, the dipole moments of atoms or molecules interact with each other and spontaneously orient themselves in a common direction to form domains. Each domain will have a different orientation. These materials when placed in an external magnetic field will force all the domains to align in the direction of the magnetic field resulting in a strong magnetization of the material. But once the field is removed, the domains will not completely revert back to their random orientation.