Three identical bars A, B and C are made of different magnetic materials. When kept in a uniform magnetic field, the field lines around them look as given in the figure. Make the correspondence of these bars with their material being diamagnetic (D), ferromagnetic (F) and paramagnetic (P).
A. $A\leftrightarrow F,B\leftrightarrow D,C\leftrightarrow P$
B. $A\leftrightarrow D,B\leftrightarrow P,C\leftrightarrow F$
C. $A\leftrightarrow F,B\leftrightarrow P,C\leftrightarrow D$
D. $A\leftrightarrow P,B\leftrightarrow F,C\leftrightarrow D$

Hint: Below material or bar can be classified by using domain theory. Diamagnetic material is the material which will repel magnetic lines so magnetic lines will go away from this kind of substance. While ferromagnetic substances are the substances which will attract magnetic lines or can say the magnetic line will attract towards the bar. Whereas magnetic lines will directly pass through the substances are known as ferromagnetic substances.

Complete step by step solution:




On basis of domain theory, substances can be classified into three category depends upon theory magnetic property:

1. Diamagnetic substances
2. Paramagnetic substances
3. Ferromagnetic substances

In this question 3 bars of different material named as A, B and C are placed in an external magnetic field.

Talking about the first figure i.e. is bar A, the magnetic lines are not only approaching but it is passing through the bar. The bar is allowing magnetic lines to pass through the bar . Such properties are exhibited in ferromagnetic substances. Hence magnet A is ferromagnetic.

Talking about the second figure i.e. is bar B, when magnetic lines in uniform magnetic fields are approaching towards bar, the magnetic lines are repelled from the bar. Such properties are exhibited by diamagnetic substances. Hence magnet B is diamagnetic. Actually when diamagnetic materials are kept in an external magnetic field, electrons which have orbital magnetic moment in the same direction as that of external magnetic field get slow down and the electrons whose orbital magnetic moment are in the opposite direction to the field speed up. As a result, diamagnetic substance is repelled by the lines of the field.
Talking about the third figure i.e. is bar C, when magnetic lines in uniform magnetic fields are approaching towards bar C, the magnetic lines are attracted towards bar C. Such properties are exhibited by paramagnetic substances. Hence bar C is paramagnetic. When a paramagnetic substance like magnet is placed in a magnetic field the tiny atomic magnet tend s to align parallel to the field. Hence they shoe temporary magnetization. The magnetic dipole movements of electrons do not get cancelled out resulting in some dipole moment of an atom. Answer: (A)

Note: Students should also know that substances can be classified by finding their magnetic susceptibility of material. Diamagnetic material has negative magnetic susceptibility while paramagnetic substances have positive and small magnetic susceptibility. Whereas ferromagnetic substances have positive and large magnetic susceptibility. Diamagnetism is universal. It is present in every material. Below critical temperature diamagnetic substances can be superconductors. You cannot use ferromagnetic substances to make permanent magnets. You can use ferromagnetic material to make permanent magnetic material or substance. But above Curie temperature ferromagnetic substance will lose its magnetism.