Question

A long straight wire is carrying current $I_1=2/5A$ in +z direction.The x - y plane contains a closed circular loop carrying current $I_2=5/2A$ and not encircling the straight wire, then the force (in newton) on the loop will be ? (Radius of the circular loop $R=3/4m$).

Answer 1

Force on a wire with current $I$ due to magnetic field $B$ is $\overrightarrow{F}$=$I(\overrightarrow{L}\times \overrightarrow{B})$

From the figure, the forces on the elements 1 and 2 are equal and opposite in direction hence they cancel each other. Similarly forces on all elements symmetric about the the dotted line cancel and net force on the loop is zero.