A ring carrying current $I$ lies in $x-z$ plane as shown. A short magnetic dipole with dipole moment directed along $x$-axis is fixed at origin. If the ring is free to move anywhere, then it will

Value of $r$ for which magnetic field at point $P$ on the axis of a circular current carrying loop of radius $a$ is maximum as shown in figure ______

Magnetic field at $O$ of a loop of uniform resistance per unit length is ______

Three infinitely long current carrying wires are placed in a plane as shown in figure. The magnetic force (in $N$) on unit length of wire- $2$ is
(Given $\frac{{\mu }_0{I}_0^2}{d}=16\pi$ in $\mathrm{SI}$ unit)