Question

A long magnetic needle of length $2L$, magnetic moment $M$ and pole strength $m$ units is broken into two pieces about an axis perpendicular to the length of the magnet at the middle point. The magnetic moment and pole strength of each piece will be

• A. $M,\frac{m}{2}$
• B. $\frac{M}{2},m$
• C. $M,m$
• D. $\frac{M}{2},\frac{m}{2}$

Answer 1

The correct option is B $\frac{M}{2},m$

Initially,

$M=mL$



When magnet is broken, new pair of dipoles with same pole strength $m$ but half the magnetic length are generated so now,


$M^{\prime }$ for each part = $m\frac{L}{2}=\left(\frac{M}{2}\right)$

So, the magnetic moment becomes half but the pole strength remains same.

Hence, option $\left(C\right)$ is the correct answer.