Question

The effective length of a magnet is $31.4\, cm$ and. its pole strength is $0.5\, Am$. If it is bent in the form of semicircle, what will be its magnetic moment then ?

• A. $0.12\,Am^{2}$
• B. $ 0.1\,A{{m}^{2}} $
• C. $0.05\,Am^{2}$
• D. $0.01\,Am^{2}$

Answer 1

Answer: (B)

On bending the magnet in the form of semicircle, let diameter of magnet is $d$. Then,
length of magnet $=\pi \frac{d}{2}$
$\therefore 31.4 =\frac{\pi d}{2}$
or $d =\frac{31.4 \times 2}{3.14}=20\, cm$
Therefore, effective length of magnet
$2 l'=d=20\, cm =0.2\, cm$
Hence, its magnetic moment will be
$M'=m \times 2 l'$
$=0.5 \times 0.2$
$=0.1\, Am ^{2}$