$A$ 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 $.........\,\times 10^{-4}\,T$.

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 $...... \, T$.

$A$ and $B$ are two concentric circular conductors with center $O$,carrying currents $i_1$ and $i_2$ as shown in the figure. If the ratio of their radii is $1:2$ and the ratio of the magnetic flux densities at $O$ due to $A$ and $B$ is $1:3$,then the value of $i_1/i_2$ is:

The magnetic induction in air at a point $1\,cm$ away from a long straight wire that carries a current of $1\,A$ will be:

$A$ long straight wire carrying a current of $30\,A$ is placed in an external uniform magnetic field of induction $4 \times 10^{-4}\,T$. The magnetic field is acting parallel to the direction of the current. The magnitude of the resultant magnetic induction in tesla at a point $2.0\,cm$ away from the wire 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