If the magnetizing field on a ferromagnetic material is increased, its permeability
(A) Decreased
(B) Increased
(C) Is unaffected
(D) May be increased or decreased

Hint: Before discussing the variation of the permeability with the magnetizing field on a ferromagnetic material, we should briefly discuss ferromagnetic materials and permeability. Permeability in general refers to the tendency of a region to be penetrated or infiltrated by fluids. Magnetic permeability is the ratio of the magnetic induction to the magnetic intensity and supports the formation of a magnetic field. Ferromagnetic substances tend to develop a strong magnetic field when placed in an external magnetic field. Having discussed the basic terminology of the question, let’s head over to the detailed solution.
Formula Used: \[\mu =\dfrac{B}{H}\]

Complete step by step solution:
As discussed above, we know that the magnetic field developed inside a ferromagnetic material depends on the externally applied field and must vary as the external field is varied. On the surface of the earth, the earth’s magnetic field acts as the external magnetic field that induces magnetism in a ferromagnetic material.
The mathematical formula of permeability states that it is a ratio of the magnetic field density to the magnetic field strength, that is
Permeability \[(\mu )=\dfrac{B}{H}\] where \[B\] is the magnetic field density and \[H\] is the magnetic field strength.
From the expression given, we can say that magnetic permeability is inversely proportional to the magnetic field strength.
Hence we can say that the permeability decreases as the magnetizing field on a ferromagnetic substance is increased.

Therefore, option (A) is the correct answer to the given question.

Note:
The magnetic permeability of material also tells us of the material’s ability to get magnetized or the material’s resistance to the applied magnetic field. Hence ferromagnetic materials are often used to form permanent magnets as they can support a large amount of magnetic flux passing through them.