Question

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

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

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 $d=\frac{31.4\times 2}{3.14}=20cm$
Therefore, effective length of magnet
$2l^{\prime }=d=20cm=0.2cm$
Hence, its magnetic moment will be
$M^{\prime }=m\times 2l^{\prime }$
$=0.5\times 0.2$
$=0.1A{m}^2$