Question

A thin magnet of magnetic of $2\pi$ units is converted into an arc of a semicircle. The new magnetic moment becomes

• A. $\pi$
• B. $2\pi$
• C. $4$
• D. $2$

Answer 1

The correct option is C $4$

When a magnet of length "l", pole strength "m" & of magnetic moment m is turned into a semi circular orc then its new magnetic moment is:
$M^{\prime }=\frac{m\times 2R=m\times 2\times 1}{\pi }=\frac{2M}{\pi }=\frac{2\times 2\text{/}\pi }{\text{/}\pi }=4$