Question

A bar magnet A of magnetic moment M_A is found to oscillate at a frequency twice that of magnet B of magnetic moment M_B when placed in a vibrating magneto-meter. We may say that

• A. $M _ { A } = 2 M _ { B }$
• B. $M _ { A } = 8 M _ { B }$
• C. $M _ { A } = 4 M _ { B }$
• D. $M _ { B } = 8 M _ { A }$

Answer 1

Answer: (C)

$M _ { A } = 4 M _ { B }$

Answer 2

$v = \frac { 1 } { 2 \pi } \sqrt { \frac { M B _ { H } } { I } } \Rightarrow v \propto \sqrt { M }$

$\Rightarrow \frac { v _ { A } } { v _ { B } } = \sqrt { \frac { M _ { A } } { M _ { B } } } \Rightarrow \frac { 2 } { 1 } = \sqrt { \frac { M _ { A } } { M _ { B } } } \Rightarrow M _ { A } = 4 M _ { B }$