A moving coil galvanometer consists of a rectangular coil of $N$ turns, each of area $A$, suspended in a radial magnetic field of flux density $B$. Derive the expression for the torque on the coil, when current $I$ passes through it. Draw a suitable labelled diagram.

Three long straight parallel wires are kept as shown in Figure. The wire $\left(3\right)$(3) carries a current $I$. The direction of flow of current $I$ in wire $\left(3\right)$, is such that the net force, on wire $\left(1\right)$, due to the other two wires is zero.

Three long straight parallel wires are kept as shown in Figure. The wire $\left(3\right)$(3) carries a current $I$. By reversing the direction of $I$, the net force, on wire $\left(2\right)$, due to the other two wires, becomes zero. What will be the directions of current $I$, in the two cases? Also, obtain the relation between the magnitudes of currents $I_1, I_2$and $I$.

A particle of mass $m$ and charge $q$ is in motion at speed $v$ parallel to a long straight conductor carrying current $I$ as shown below.

Find the magnitude and direction of electric field required so that the particle goes undeflected.