The magnetic field at the Centre of a circular coil of a radius $r$ is $\pi$ times that due to a long straight wire at a distance $r$ from it, for equal currents. The following figures show three cases: in all cases, the circular part has a radius $r$ and straight ones are infinitely long. For the same current, the $B$ field at the Centre $P$ in case of diagrams $1$, $2$ and $3$ has the ratio

A cell is connected between the points $A$ and $C$ of a circular conductor $A B C D$ of Centre $O$ with angle $AOC=60°$. If $B_1$ and $B_2$ are the magnitudes of the magnetic fields at $O$ due to the currents in $A B C$ and $A D C$ respectively, the ratio $\frac{B_1}{B_2}$ is

In the given figure, net magnetic field at $O$ will be,

The unit vectors $\hat{i}$, $\hat{j}$ and $\hat{k}$ are as shown below. What will be the magnetic field at $O$ in the following figure?

(Current flowing through wire $=i$)

For the current-carrying wire, show that the magnetic field at $P$ is,

$L$ is the circular ring made of a uniform wire. Current enters and leaves the ring through straight conductors which, if produced, would have passed through the centre $C$ of the ring. The magnetic field at $C$ is

Figure shows a long wire bent at the middle to form a right angle.