Question

A magnetic wire of dipole moment $4\pi \, Am^{2}$ is bent in the form of semicircle. The new magnetic moment is

• A. $4\pi \, Am^{2}$
• B. $8\pi \, Am^{2}$
• C. $4 \, \text{A }\text{m}^{2} \, $
• D. $8 \, \text{A }\text{m}^{2} \, $

Answer 1

Answer: (D)

Here, $M_i=4 \pi$
$m L=4 \pi $
$m=\frac{4 \pi}{L}$
The new distance between poles is
$L_1=2 r=2 \frac{L}{2 \pi}=\frac{L}{\pi} $
$\therefore M_f=m L_1=\frac{m L}{\pi}=\frac{4 \pi}{\pi}=4 \mathrm{~A} \mathrm{~m}^2$