$PQRS$ is a square loop made of a uniform conducting wire. The current enters the loop at $P$ and leaves at $S$. Then the magnetic field will be

In the diagram,$I_{1}$ and $I_{2}$ are the strengths of the currents in the loop and straight conductor,respectively. Given $OA = AB = R$. The net magnetic field at the centre $O$ is zero. Then the ratio of the currents in the loop and the straight conductor is:

Two straight infinitely long current-carrying wires are kept along the $z-$axis at the coordinates $(0, a, 0)$ and $(0, -a, 0)$ respectively, as shown in the figure. The current in each wire is equal and directed along the negative $z-$axis (into the plane of the paper). The variation of the magnetic field on the $x-$axis will be approximately:

$A$ steady current flows in a long wire. It is bent into a circular loop of one turn and the magnetic field at the centre of the coil is $B$. If the same wire is bent into a circular loop of $n$ turns, the magnetic field at the centre of the coil is

Which law is useful to determine the relation between current and the magnetic field produced by it?

$\frac{V \cdot s}{A \cdot m}$ is the unit of which physical quantity?