A square loop of side 2 a, and carrying current I, is kept in XZ plane with its centre at origin. A long wire carrying the same current I is placed…

A square loop of side $\displaystyle 2$ a, and carrying current I , is kept in XZ plane with its centre at origin. A long wire carrying the same current I is placed parallel to the $\displaystyle z$-axis and passing through the point $\displaystyle (0, b, 0)$, $\displaystyle (\mathrm{b} \gg \mathrm{a})$. The magnitude of the torque on the loop about $\displaystyle z$-axis is given by :