Question

A wire of length $L$ metre carrying a current of $I$ ampere is bent in the form of a circle. Its magnetic moment is,

• A. $I \,L^{2} /4 \,A\, m^{2}$
• B. $1\,\pi\,L^{2}/4\,A\,m^{2}$
• C. $2\,I\,L^{2}/\pi\, A\,m^{2}$
• D. $I\,L^{2}/4\pi\,A\,m^{2}$

Answer 1

Answer: (D)

$2\pi\,r=L$
$r=\frac{L}{2\pi}$
$M=I (A)$
$M=I (\pi\,r^{2})$
$M=I \left(\pi\right) \left(\frac{L}{2\pi}\right)^{2}$
$M=\frac{IL^{2}}{4\pi}$