Two parallel wires $1 \text{ m}$ apart carry currents of $1 \text{ A}$ and $3 \text{ A}$ respectively in opposite directions. The force per unit length acting between these two wires is

$A$ square loop of side $a$ hangs from an insulating hanger of a spring balance. The magnetic field of strength $B$ exists only at the lower edge. It carries a current $I$. Find the change in the reading of the spring balance if the direction of current is reversed.

$A$ 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.

The magnetic field existing in a region is given by $\vec B = B_0 [1 + \frac{x}{l}] \hat k$. $A$ square loop of edge $l$ carrying current $I_0$ is placed with its edges parallel to the $x-y$ axes. Find the magnitude of the net magnetic force experienced by the loop.

$A$ current-carrying wire $LN$ is bent as shown below. If the wire carries a current of $10 \, A$ and is placed in a magnetic field of $5 \, T$ which acts perpendicular to the paper outwards,then it will experience a force of ......... $N$.

Three long straight wires are carrying current as shown in the diagram. The magnetic force per unit length on wire $Q$ is $..... \times 10^{-7} \ N/m$.