Answer the following questions:(a) Why does a paramagnetic sample display greater magnetisation(for the same magnetising field) when cooled? (b) Why is diamagnetism, in contrast, almost independent oftemperature? (c) If a toroid uses bismuth for its core, will the field in the core be(slightly) greater or (slightly) less than when the core is empty? (d) Is the permeability of a ferromagnetic material independent ofthe magnetic field? If not, is it more for lower or higher fields? (e) Magnetic field lines are always nearly normal to the surface of aferromagnet at every point. (This fact is analogous to the staticelectric field lines being normal to the surface of a conductor atevery point.) Why? (f ) Would the maximum possible magnetisation of a paramagneticsample be of the same order of magnitude as the magnetisationof a ferromagnet?
a)
In a paramagnetic material, the magnetic dipoles are randomly aligned. As the material is heated, the molecules gain energy and the alignment of dipoles gets further disrupted. Thus, the material shows weaker magnetization when heated. As the material is cooled down, the disruption in alignment of dipoles is reduced, hence, the dipoles get aligned and the material displays stronger magnetization.
b)
In a diamagnetic material, the induced dipole moments are always opposite to the magnetizing field. Hence, the overall magnetic behavior of material is not affected by the internal motion of the atoms (which is related to the temperature). Thus, temperature does not affect the diamagnetism of a material.
c)
Bismuth is a diamagnetic material. A toroid using bismuth for its core will have higher field when the core is empty because, the bismuth in the core will neutralize some of the field produced.
d)
Consider the magnetization curve of a ferromagnetic material.
It is observed that the permeability of the material changes with change in magnetic field. Moreover, at higher currents, the increase in magnetic field is almost negligible. Thus permeability is higher for lower fields.
e)
For a ferromagnetic material, the permeability is very high, μ ≫ 1 . At the interface of two mediums, when one the media has very high permeability, the field lines meet this medium nearly normally to its surface.
f)
The maximum possible magnetization of a paramagnetic sample can be of the same order of magnitude as the magnetization of a ferromagnetic sample apart from some minor differences in strength of the individual atomic dipoles of the different materials. However, due to saturation effects, the required magnetic field will be impractically high.
a)
In a paramagnetic material, the magnetic dipoles are randomly aligned. As the material is heated, the molecules gain energy and the alignment of dipoles gets further disrupted. Thus, the material shows weaker magnetization when heated. As the material is cooled down, the disruption in alignment of dipoles is reduced, hence, the dipoles get aligned and the material displays stronger magnetization.
b)
In a diamagnetic material, the induced dipole moments are always opposite to the magnetizing field. Hence, the overall magnetic behavior of material is not affected by the internal motion of the atoms (which is related to the temperature). Thus, temperature does not affect the diamagnetism of a material.
c)
Bismuth is a diamagnetic material. A toroid using bismuth for its core will have higher field when the core is empty because, the bismuth in the core will neutralize some of the field produced.
d)
Consider the magnetization curve of a ferromagnetic material.
It is observed that the permeability of the material changes with change in magnetic field. Moreover, at higher currents, the increase in magnetic field is almost negligible. Thus permeability is higher for lower fields.
e)
For a ferromagnetic material, the permeability is very high,
f)
The maximum possible magnetization of a paramagnetic sample can be of the same order of magnitude as the magnetization of a ferromagnetic sample apart from some minor differences in strength of the individual atomic dipoles of the different materials. However, due to saturation effects, the required magnetic field will be impractically high.
