question_answer 16)

Answer the following questions: (a) Why does a paramagnetic sample display greater magnetization (for the same magnetizing field) when cooled? (b) Why is diamagnetism, in contrast, almost independent of temperature? (c) If a toroid used bismuth for its core, will the field in the core be (slightly) greater of (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 of higher field? (e)Magnetic field lines are always nearly normal to the surface of a ferromagnetic 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 magnetization of a paramagnetic sample be of the same order of magnitude as the magnetization of ferromagnetic?  

Answer:

(a)At lower temperatures, the tendency of dealignments of magnetic dipoles with magnetizing field is reduced because of decrease in their random thermal motion.                 (b) The induced dipole moment in a diamagnetic sample is opposite to the magnetizing field irrespective of the internal thermal motion of the atoms. Thus diamagnetism is independent of the changes in temperature.                 (c) It will be slightly less because bismuth is a diamagnetic substance.                 (d) Permeability of a ferromagnetic material depends on applied magnetic field. Permeability is more for lower magnetic field.                 (e) When two media are considered and one of these hasthen magnetic field lines meet normally to this medium. Proof of this fact is available from the boundary conditions of magnetic fields (strength of magnetic field B and magnetising intensity H) at the interface of two media.                 (f) The maximum possible magnetisation of a paramagnetic sample would be of the same order of magnitude as the magnetisation of a ferromagnetic sample but the paramagnetic sample requires very high magnetising field which may not be practically possible.