Question

The relative permeability of _________ materials is slightly less than unity.
1. anti-ferrimagnetic
2. diamagnetic
3. paramagnetic
4. Ferromagnetic

Answer 1

Correct Answer - Option 2 : diamagnetic

• Magnetic permeability: relative increase or decrease in the resultant magnetic field inside a material compared with the magnetizing field in which the given material is located.
• It is the property of a material that is equal to the magnetic flux density B established within the material by a magnetizing field divided by the magnetic field strength H of the magnetizing field. Magnetic permeability is thus defined as μ = B/H.
• A diamagnetic material has a constant relative permeability slightly less than 1. When a diamagnetic material such as bismuth is placed in a magnetic field, the external field is partly expelled then the magnetic flux density within it is slightly reduced.
• A paramagnetic material has a constant relative permeability slightly more than 1. When a paramagnetic material such as platinum is placed in a magnetic field, it becomes slightly magnetized in the direction of the external field.
• A ferromagnetic material such as iron does not have a constant relative permeability. The permeability of ferromagnetic materials varies greatly with field strength. As the magnetizing field increases, the relative permeability increases, reaches a maximum, and then decreases.
• In free space the magnetic flux density is the same as the magnetizing field because there is no matter to modify the field. The permeability B/H of space is dimensionless and has a value of 1.

 

Note:

Material	Magnetic Susceptibility (Xm­)	Relative Permeability (Km = 1 + Xm)	Magnetic Permeability (μm = Kmμ0)
Diamagnetic	-10-5 to -10-9	< 1	μm < μ0
Paramagnetic	10-5 to 10-3	> 1	μm > μ0
Ferromagnetic	≫ 1	≫ 1	μm ≫ μ0