What is the source of a magnetic field?

$A$ circular arc of radius $r$ carrying current $I$ subtends an angle $\frac{\pi}{8}$ at its centre. The radius of the metal wire is uniform. The magnetic induction at the centre of the circular arc is ($\mu_0 =$ permeability of free space).

$A$ straight wire of length $\pi^2 \, m$ carries a current of $2 \, A$. The magnetic field due to it is measured at a point $1 \, cm$ away from it. If the wire is bent into a circle and carries the same current,what is the ratio of the magnetic field at its centre to the magnetic field measured in the first case?

The magnetic field at the centre $O$ of a square loop of side $a$ carrying current $I$ as shown in the figure is:

$A$ current of $0.1\, A$ circulates around a coil of $100$ turns and having a radius equal to $5\, cm$. The magnetic field set up at the centre of the coil is $(\mu_0 = 4\pi \times 10^{-7} \, Wb/A \cdot m)$

$A$ straight wire carrying a current of $14\,A$ is bent into a semicircular arc of radius $2.2\,cm$ as shown in the figure. The magnetic field produced by the current at the centre $(O)$ of the arc is $.........\,\times 10^{-4}\,T$.