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 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 ferreomgnet at every point . (This fact is analogous to the static electric field lines being normal to the surface of conductor at every point). Why ?
f. Would the maximum possible magnetisation of paramagnetic sample be of the same order of magnitude as the magnetisation of ferromagnet ?

Explanation

a. The susceptibility X increases.
b. The induced magnetic moment of electrons oppose the external field.
c. Bismuth being diamagnetic , field will be slightly less than the field in its absence.
d. No. it is greater for lower fields.
e. `mu` for ferromagnetic is very largc. The lines of force on the surface area and by repulsion take normal shape.
f. Yes. But only under extremely high magnetising field .