Three long straight and parallel wires carrying currents are arranged as shown in the figure. The force experienced by $10 \mathrm{cm}$ length of wire $Q$ is,

Two long parallel wires separated by $0.1 \mathrm{m}$ carry currents of $1 \mathrm{A}$ and $2 \mathrm{A}$, respectively in opposite directions. A third current-carrying wire parallel to both of them is placed in the same plane such that it feels no net magnetic force. It is placed at a distance of, 

Two very long straight wires are set parallel to each other. Each carries a current $I$ in the same direction and the separation between them is $2r$. The intensity of magnetic field at point $P$ as shown in figure is,

Two parallel very long straight wires carrying current of $5 \mathrm{A}$ each are kept at a separation of $1 \mathrm{m}$. If the currents are in the same direction, the force per unit length between them is $\left(\text{in} \mathrm{N} {\mathrm{m}}^{-1}\right)$ $\left( \mathrm{Take} {\mu }_0=4\pi \times {10}^{-7} \mathrm{Sl}\right)$

Two long straight wires, each carrying current of $5.0 \mathrm{A}$, are kept parallel to each other at a separation of $2.5 \mathrm{cm}$. The magnitude of magnetic force experienced by $5.0 \mathrm{cm}$ of a wire is

An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current $i$ along the same direction as shown in the figure. The magnitude of force per unit length on the middle wire $B$ is given by 

A pair of stationary and infinitely long bent wires are placed in the x-y plane as shown in the figure. The two wires carry currents of $4 \mathrm{A}$ and $9 \mathrm{A}$ If the segment $D$ and $A$ are along the x-axis and the segments $C$ and $F$ are parallel to y-axis such that $OB=2 \mathrm{cm}$ and $OE=3 \mathrm{cm}$, then the magnitude of the magnetic induction at the origin '$O$' is $\left({\mu }_0=4\mathrm{\pi }\times {10}^{-7} \mathrm{H} {\mathrm{m}}^{-1}\right)$

A rectangular loop carrying a current $I$ is placed in a uniform magnetic field $B$. The area enclosed by the loop is $A$. If there are $n$ turns in the loop, the torque acting on the loop is given by