The magnetic induction at the centre of a current-carrying circular coil of radius $r$ is

The magnetic field at the point of intersection of diagonals of a square wire loop of side $L$ carrying a current $I$ is

When a certain length of wire is turned into one circular loop,the magnetic induction at the centre of the coil due to a current $I$ flowing through it is $B_1$. If the same wire is turned into three loops to make a circular coil,the magnetic induction at the center of this coil for the same current will be:

The magnitude of the magnetic field (in $SI$ units) at the centre of a hexagonal coil of side $10 \, cm$, having $50$ turns and carrying a current $I$ (Ampere), in units of $\frac{\mu_{0} I}{\pi}$ is: (in $\sqrt{3}$)

$A$ horizontal overhead powerline is at a height of $4\ m$ from the ground and carries a current of $100\ A$ from east to west. The magnetic field directly below it on the ground is: (Given: $\mu_0 = 4\pi \times 10^{-7} \, T \cdot m/A$)

$A$ rod with a circular cross-section area $2 \text{ cm}^2$ and length $40 \text{ cm}$ is wound uniformly with $400$ turns of an insulated wire. If a current $0.4 \text{ A}$ flows in the wire winding, the total magnetic flux produced inside the winding is $4\pi \times 10^{-6} \text{ Wb}$. The relative permeability of the rod is (Given permeability of vacuum $\mu_0 = 4\pi \times 10^{-7} \text{ N m A}^{-2}$)