$A$ loop in the form of four connected semi-circular wires carrying current $I$ lies in the $x-y$ plane as shown in the figure. The unit vector $\hat{k}$ is coming out of the plane of the paper. The magnetic moment of the current loop is

  • A
    $a^2 I \hat{k}$
  • B
    $\left( \frac{\pi}{2} + 1 \right) a^2 I \hat{k}$
  • C
    $-\left( \frac{\pi}{2} + 1 \right) a^2 I \hat{k}$
  • D
    $\left( 2\pi + 1 \right) a^2 I \hat{k}$

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