Question

A long magnetic needle of length $2L$, magnetic moment $M$ and pole strength $m$ units is broken into two pieces at the middle. The magnetic moment and pole strength of each piece will be:

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

Answer 1

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

Given that,

Length $l=2L$

Pole strength $=m$

Now, the magnetic moment is

$M=mL$

Now, if cut perpendicular to the axis of magnetic needle

New length $l^{\prime }=L$

New pole strength $m^{\prime }=m$

Now, new magnetic moment is

$M^{\prime }=\frac{mL}{2}$

$M^{\prime }=\frac{M}{2}$

Hence, the magnetic moment of each part is $\frac{M}{2}$ and pole strength of each part is $m$