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 magnetometer. 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)

$v=\frac{1}{2 \pi} \sqrt{\frac{M B_{H}}{I}}$
$\Rightarrow v \propto \sqrt{M}$
$\Rightarrow \frac{v_{A}}{v_{B}}=\sqrt{\frac{M_{A}}{M_{B}}}$
$\Rightarrow \frac{2}{1}=\sqrt{\frac{M_{A}}{M_{B}}}$
$\Rightarrow M_{A}=4 M_{B}$