An electron in a hydrogen atom revolves around its nucleus with a speed of $6.76 \times 10^6 \, m/s$ in an orbit of radius $0.52 \, \mathring{A}$. The magnetic field produced at the nucleus of the hydrogen atom is $...... \, T$.

Write the formula for the force per unit length between two parallel,current-carrying conducting wires.

Two points $A$ and $B$ on the axis of a circular current loop are at distances of $4 \ cm$ and $3 \sqrt{3} \ cm$ from the centre of the loop. If the ratio of the induced magnetic fields at points $A$ and $B$ is $216: 125$, the radius of the loop is (in $cm$)

$A$ current carrying circular coil of radius $R$ has a point $P$ situated on its axis at a distance $x$ from its centre $O$ of the coil. The magnetic induction at point $P$ is $\left(\frac{1}{8}\right)^{\text{th}}$ of the magnetic field at its centre $O$. The value of $x$ is

$A$ steady current flows in a long wire. It is bent into a circular loop of one turn and the magnetic field at the centre of the coil is $B$. If the same wire is bent into a circular loop of $n$ turns, the magnetic field at the centre of the coil is

The correct Biot-Savart law in vector form is