Which law is useful to determine the relation between current and the magnetic field produced by it?

The electric current in a circular coil of four turns produces a magnetic induction $32 \ T$ at its centre. The coil is unwound and is rewound into a circular coil of a single turn. If the same current flows through the new coil,the magnetic induction at the centre will be $.......... \ T$.

For a wire, as shown in the figure, carrying a current of $10 \,A$, find the magnetic induction field at the point $O$. (Given: $\mu_0 = 4 \pi \times 10^{-7} \,H/m$)

If the current flowing through the shell of the previous objective is equal to $i$,then the energy density at a point at a distance $2R$ from the axis of the shell varies according to which graph?

The magnetic field at the centre of a current-carrying circular loop of radius $R$ is $16 \ \mu T$. The magnetic field at a distance $x = \sqrt{3}R$ on its axis from the centre is . . . . . . $\mu T$.

What is the ratio of the electric field to the magnetic field produced by a moving point charge if its speed is $4.5 \times 10^{5} \; m/s$?