Question

If a bar magnet of pole strength $m$ and magnetic moment $M$ is cut perpendicular to its axis in two equal halves then its new pole strength $m ^{\prime}$ and magnetic moment $M ^{\prime}$ are respectively

• A. $m ^{\prime}= m$ and $M ^{\prime}= M$
• B. $m ^{\prime}= m$ and $M ^{\prime}=\frac{ M }{2}$
• C. $m ^{\prime}=\frac{ m }{2}$ and $M ^{\prime}=2 M$
• D. $m ^{\prime}=2 m$ and $M ^{\prime}=\frac{ M }{2}$

Answer 1

Answer: (B)

When a bar magnet cut perpendicular to its axis into two equal parts then $m ^{\prime}= m$ and length $\ell^{\prime}=\frac{\ell}{2}$
$\therefore M = m \ell= m \frac{\ell}{2}=\frac{ M }{2}$