$A$ straight wire is placed in a magnetic field that varies with distance $x$ from the origin as $\vec{B} = B_0 \left( 2 - \frac{x}{a} \right) \hat{k}$. The ends of the wire are at $(a, 0)$ and $(2a, 0)$ and it carries a current $I$ in the positive $x$-direction. If the force on the wire is $\vec{F} = IB_0 \left( \frac{ka}{2} \right) \hat{j}$,then the value of $k$ is:

Three long,straight parallel wires carrying currents are arranged as shown. The wire $C$ which carries a current of $5.0 \text{ A}$ is so placed that it experiences no force. The distance of wire $C$ from wire $D$ is (in $cm$)

$A$ current of $10 \text{ A}$ flows through a horizontal straight wire $A$ with both ends rigidly fixed. Wire $B$ is placed directly above and parallel to $A$. The weight per unit length of wire $B$ is $40 \times 10^{-3} \text{ N/m}$ and it carries a current of $20 \text{ A}$. Find the distance of wire $B$ from wire $A$ so that wire $B$ remains at rest. Also,state the direction of current flowing through it.

Two long straight parallel conductors separated by a distance of $0.5\,m$ carry currents of $5\,A$ and $8\,A$ in the same direction. The force per unit length experienced by each other is

Through two parallel wires $A$ and $B$,$10 \, A$ and $2 \, A$ of currents are passed respectively in opposite directions. If the wire $A$ is infinitely long and the length of the wire $B$ is $2 \, m$,the force on the conductor $B$,which is situated at a $10 \, cm$ distance from $A$,will be:

An arbitrarily shaped closed coil is made of a wire of length $L$ and a current $I$ ampere is flowing in it. If the plane of the coil is perpendicular to a uniform magnetic field $\vec{B}$, the net magnetic force on the coil is