Question 5.16: 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 of temperature? (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 of the magnetic field? If not, is it more for lower or higher fields? (e) Magnetic field lines are always nearly normal to the surface of a ferromagnet at every point. (This fact is analogous to the static electric field lines being normal to the surface of a conductor at every point.) Why? (f ) Would the maximum possible magnetisation of a paramagnetic sample be of the same order of magnitude as the magnetization of a ferromagnet?
Class 12 - Physics - Magnetism And Matter Magnetism And Matter Page-202
Answers
(b) in diamagnetics, the molecular dipole moments always align in the direction opposite to that of external magnetising field , inspite of the internal motion of atoms.
(c) As bismuth is diamagnetic in nature,bso the field in the toroid with bismuth core will be slightly less than when core is empty.
(d) No, the permeability of a ferromagnetic material is not independent of the magnetic field. it is more at higher fields.
(e) As the magnetic permeability of a ferromagnetic is much larger than unity. so the magnetic field lines are always nearly normal to the surface of a ferromagnet at every point.
(f) Yes, but for the maximum possible magnetisation of paramagnetic sample, impractically very high magnetising field are required.
(a) Disturbance is minimized while cooling.
(b) Molecules does not impact the material's diamagnetism.
(c) Less magnetic field than a toroid
(d) Not distinct from the magnetic field
(e) Magnetic field lines are still almost natural at any point
(f) Yes
Explanation:
(a) The orientations of the dipoles are disturbed at high temperatures due to the spontaneous thermal activity of the molecules. This disturbance is minimized while cooling. Therefore, when cooled a paramagnetic specimen displays better magnetisation.
(b) Every diamagnet material molecule is not in itself a magnetic dipole. Therefore, the spontaneous thermal motion of the diamagnetic material's molecules does not impact the material's diamagnetism.
(c) Bismuth is a material of diamagnesis. Therefore a toroid with a bismuth core has a significantly less magnetic field than a toroid whose center is empty.
(d) The ferromagnetic materials ' permeability is not distinct from the magnetic field applied. It is bigger for a smaller area.
(e) A ferromagnetic material has always greater permeability than one. Therefore, the magnetic field lines are still almost natural at any point to the surface of these materials. The proof for this statement is based on the magnetic field boundary conditions at the interface of 2 media
(f) Yes, the highest magnetisation possible for a paramagnetic sample would be of the similar order of magnitude as a ferromagnet's magnetisation. That requires high density magnetisation fields.
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