question_answer

A magnet of magnetic moment M and pole strength m is divided in two equal parts, then magnetic moment of each part will be  [MP Board 1985; MP PET 1984, 2000;  NCERT 1974;  AFMC 1996; MP PMT 2002; MH CET (Med.) 2001; CPMT 1983, 84; KCET 1994, 2001]

A)            \[M\]                                      

B)            \[M/2\]

C)            \[M/4\]                                  

D)            \[2M\]

Correct Answer: B

Solution :

           If cut along the axis of magnet of length l, then new pole strength \[{m}'=\frac{m}{2}\]and new length \[{l}'=l\] \[\therefore \]New magnetic moment \[{M}'=\frac{m}{2}\times l=\frac{ml}{2}=\frac{M}{2}\] If cut perpendicular to the axis of magnet, then new pole strength \[{m}'=m\] and new length, \[{l}'=l/2\] \[\therefore \] New magnetic moment \[{M}'=m\times \frac{l}{2}=\frac{ml}{2}=\frac{M}{2}\]