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, 

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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 

Which of the following graphs shows the variation of magnetic induction $B$ with distance $r$ from a long wire carrying current