Question

Two magnets A and B are identical in mass, length and breadths but have different magnetic moments. In a vibration magnetometer, if the time period of B is twice the time period of A. The ratio of the magnetic moments $M _ { A } / M _ { B }$ of the magnets will be

• A. $1 / 2$
• B. $2$
• C. $4$
• D. $1 / 4$

Answer 1

Answer: (C)

$4$

Answer 2

$T = 2 \pi \sqrt { \frac { I } { M B _ { H } } } \Rightarrow T \propto \frac { 1 } { \sqrt { M } } \Rightarrow \frac { M _ { A } } { M _ { B } } = \left( \frac { T _ { B } } { T _ { A } } \right) ^ { 2 } = \frac { 4 } { 1 }$