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# A closely wound solenoid of $2000$ turns and area of cross section $1.6 \times 10^{-4}m^2$, carrying a current of $4.0\;A$ is suspended through its center allowing it to turn in a horizontal plane. What is the magnetic moment associated with the solenoid ?

$\begin{array}{1 1} 128\;J/T \\ 12.8\;J/T \\ 1.28\;J/T \\ 0.128\;J/T \end{array}$

Given $n= 2000$
$A= 1.6 \times 10^{-4} m^2$
$I=4A$
$\therefore M= nIA$
$\qquad= 2000 \times 1.6 \times 10^{-4} \times 4$
$\qquad= 1.28 J/T$
Answer : $1.28 J/T$