Q. A wire of length $l$ metre carrying a current $i$ ampere is bent in the form of a coil having two turns. Its magnitude of magnetic moment will be
A) $il/4\ \pi$
B) $i^{2}l^{2}/4\pi$
C) $i^{2}l/8\pi$
D) $il^{2}/8\pi$
Explanation
(d) If $r\ $ is the radius of the circle, then
$l = 2\pi r \times 2\ \ \ \ \ \ or\ \ r = \frac{1}{4\pi}$
Area $= \ \pi r^{2} = \pi l^{2}/16\pi^{2} = l^{2}/16\pi$
Magnetic moment $= \ n\ IA = 2Il^{2}$/16$\ \pi = Il^{2}$/8$\ \pi$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.