Q. A steel wire of length $l$ has a magnetic moment M. It is bent in L - shape (Figure). The new magnetic moment is

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A

$M$

B

$\frac{M}{\sqrt{2}}$

C

$\frac{M}{2}$

D

$2M$

Solution:

Magnetic moment, $M=ml$
$\frac{M}{l}=m,$ where m is the pole strength. Therefore distance between poles
$= \, \sqrt{\left(\frac{l}{2}\right)^{2} + \left(\frac{l}{2}\right)^{2}}=\frac{l}{\sqrt{2}}$
So, $M^{′}=\frac{m l}{\sqrt{2}}=\frac{M}{\sqrt{2}}$

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