$A$ tightly wound coil of $200$ turns and of radius $20 \ cm$ carries a current of $5 \ A$. The magnetic field at the centre of the coil is:

An infinitely long wire,located on the $z$-axis,carries a current $I$ along the $+z$-direction and produces the magnetic field $\vec{B}$. The magnitude of the line integral $\int \vec{B} \cdot d\vec{l}$ along a straight line from the point $(-\sqrt{3} a, a, 0)$ to $(a, a, 0)$ is given by [$\mu_0$ is the magnetic permeability of free space.]

Give the $SI$ unit of magnetic field from the Biot-Savart law.

$A$ circular arc of wire of radius of curvature $r$ subtends an angle of $\frac{\pi}{5}$ radian at its centre. If current $i$ is flowing in it, then the magnetic induction at its centre is ($\mu_0$ = permeability of free space).

$20 \, A$ current is flowing in a long straight wire. The intensity of the magnetic field at a distance of $20 \, cm$ from the wire will be:

$A$ circular coil of radius '$r$' and number of turns '$n$' carries a current '$I$'. The magnetic fields at a small distance '$h$' along the axis of the coil $(B_a)$ and at the centre of the coil $(B_c)$ are measured. The relation between $B_c$ and $B_a$ is