A straight wire of length $\left({\pi }^2\right)$  metre is carrying a current of $2 \mathrm{A}$ and the magnetic field due to it is measured at a point distant $1 \mathrm{cm}$ from it. If the wire is to be bent into a circle and is to carry the same current as before, the ratio of the magnetic field at its centre to that obtained in the first case would be 

 

The magnetic field at the centre of coil of $n$ turns, bent in the form of a square of side $2l$ carrying current $i$, is, 

Two identical wires $A$ and $B$, each of length $4$ carry the same current $I$. Wire A bent into a circle of radius $R$ and wire $B$ is bent to form a square of the side $a$. If $B_{\mathrm{A}}$ and $B_{\mathrm{B}}$ are the values of the magnetic field at the centers of the circle and square respectively, then the ratio $\frac{B_{\mathrm{A}}}{B_{\mathrm{B}}}$ is

A length $L$ of wire carrying current $I$ is to be bent into a circle or a square, each of one turn. The ratio of $B_{\mathrm{g}}$ (greater) to $B_{\mathrm{s}}$ (smaller) is nearly, 

A current-carrying thin uniform wire of length $4l$  is bent like a square so that it produces a magnetic induction $B_1$ at the centre of the square. When the same wire is bent like a circle, it produces a magnetic induction $B_2$ at the centre of the circle. The ratio between $B_1$and $B_2$ is,

A long conducting wire carrying a current $I$ is bent at $120°$ (see figure). The magnetic field $B$ at a point $P$ on the right bisector of bending angle at a distance $d$ from the bend is $\left({\mu }_0\right.$is the permeability of free space)

Current $I$ is flowing in a conductor shaped as shown in the figure. The radius of the curved part is $r$ and the length of straight portion is very large. The value of the magnetic field at the centre $o$ will be

The magnetic induction at the centre $O$ in the figure shown is 

Two long parallel wires $P$ and $Q$ are both perpendicular to the plane of the paper with distance $5 \mathrm{m}$ between them. If $P$ and $Q$ carry current of $2.5 \mathrm{A}$ and $5 \mathrm{A}$ respectively in the same direction, then the magnetic field at a point half way between the wires is