Question

A wire of length $ L $ metre carrying a current $ I $ ampere is bent in the form of a circle. The magnitude of its magnetic moment is :

• A. $ IL^2/4\pi $
• B. $ {{I}^{2}}{{L}^{2/}}4\pi $
• C. $ {{I}^{2}}L/8\pi $
• D. $ I{{L}^{2}}/8\pi $

Answer 1

Answer: (A)

If $r$ is the radius of circle then $L=2 \pi r$
or $r=\frac{L}{2 \pi}$
$ \therefore $ Area $=\pi r^{2}$
$=\pi L^{2} / 4 \pi^{2}=\frac{L^{2}}{4 \pi}$
Now magnetic moment $M=N i A$
$=I L^{2} / 4 \pi$