question_answer

If the magnetic dipole moment of an atom of diamagnetic material, paramagnetic material and ferromagnetic material are denoted by\[{{\mu }_{d}},\,{{\mu }_{p}}\]and \[{{\mu }_{f}}\]respectively, then

A) \[{{\mu }_{d}}\ne 0\]and\[{{\mu }_{f}}\ne 0\]    

B) \[{{\mu }_{p}}\ne 0\] and \[{{\mu }_{f}}\ne 0\]

C)  \[{{\mu }_{d}}\ne 0\]and \[{{\mu }_{p}}\ne 0\] 

D)  \[{{\mu }_{d}}\ne 0\]and\[{{\mu }_{p}}\ne 0\] 

Correct Answer: B

Solution :

 In diamagnetic substances in each pair of electrons, the spins of both the electrons are in opposite directions. Hence, the electrons of each pair completely cancel the magnetic moment of each other. Thus, the net magnetic moment of each atom of such substances is zero, i.e., \[{{\mu }_{d}}=0.\] The property of paramagnetism is found in those substances whose atoms or molecules have an excess of electrons spinning in the same direction. Hence, atoms of paramagnetic substances have permanent magnetic moment, i.e., \[{{\mu }_{p}}\ne 0.\] The property of ferromagnetism is found in substances which acquire very strong magnetism  when placed in an external magnetic field. Like the paramagnetic substances each atom of ferromagnetic substances also has a permanent magnetic moment, i.e., \[{{\mu }_{f}}\ne 0.\]