Question

A steel wire of length 0.28 m is magnetised and is found to have moment of 0.308 A.m${}^2$. If it is bent into a semi circle, its new magnetic moment is :

• A. 0.196Am${}^2$
• B. 0.308Am${}^2$
• C. 0.392Am${}^2$
• D. 0.09Am${}^2$

Answer 1

The correct option is A 0.196Am${}^2$

Magnetic moment will remain constant $\frac{\pi }{2}{L}_2=L_1$

$L_2=\frac{2}{\pi }{L}_1$

$\mu =PL$

${\mu }_1=P{L}_1$

${\mu }_2=P{L}_2$

$\frac{{\mu }_1}{{\mu }_2}=\frac{L_1}{L_2}$

$\frac{0\cdot 308}{{\mu }_2}=\frac{L_1}{L_2}=\frac{\pi }{2}$

${\mu }_2=\frac{0\cdot 308\times 2}{\pi }$

${\mu }_2=0\cdot 196A{m}^2$