Following is a square shape loop, whose one arm BC produces a magnetic field $B$ at the center of the coil. The resultant magnetic field due to all the arms will be:- 

                                                     

A wire is parallel to one arm of a square current-carrying loop, which also carries current. Now at any point $A$ within the coil, the magnetic field will be:-

Assume the given diagram a combination of complete circle and two semi-infinite wires. Magnetic field at point $\mathrm{O}$ will be:

 $A$ and $B$ are two concentric circular loops carrying current $i_1$ and $i_2$ as shown in figure. If ratio of their radii is $1:2$ and ratio of the flux densities at the centre $O$ due to $A$ and $B$ is $1:3$ then the value of $\frac{i_1}{i_2}$ will be 

For the given current distribution the magnetic field at point, $P$ is