question_answer

An iron rod of length L and magnetic moment M is bent in the form of a semicircle. Now its magnetic moment will be             [CPMT 1984; MP Board 1986; NCERT 1975; MP PET/PMT 1988; EAMCET (Med.) 1995; Manipal MEE 1995;RPMT 1996; BHU 1995; MP PET 2002]

A)            \[M\]                                      

B)            \[\frac{2M}{\pi }\]

C)            \[\frac{M}{\pi }\]               

D)            \[M\pi \]

Correct Answer: B

Solution :

                   On bending a rod it?s pole strength remains unchanged where as its magnetic moment changes. New magnetic moment \[{M}'=m(2R)=m\left( \frac{2L}{\pi } \right)=\frac{2M}{\pi }\]