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

In a hydrogen atom,an electron is revolving at $6.6 \times 10^{15} \text{ rev/s}$ around the nucleus in an orbit of radius $0.47 \text{ Å}$. The magnetic field induction produced at the centre of the orbit is nearly: (in $\text{ Wb m}^{-2}$)

$A$ current $I$ flows in a circular arc of radius $r$ subtending an angle $\theta$ at the centre $O$ as shown in the figure. Find the magnetic field at the centre $O$ of the circle.

Five very long,straight wires are bound together to form a small cable. Currents carried by the wires are $I_1 = 20\,A, I_2 = -6\,A, I_3 = 12\,A, I_4 = -7\,A, I_5 = 18\,A.$ The magnetic induction at a distance of $10\,cm$ from the cable is

Current through $ABC$ and $A^{\prime} B^{\prime} C^{\prime}$ is $I$. What is the magnetic field at $P$? $BP = PB^{\prime} = r$. (Here $C^{\prime} B^{\prime} PBC$ are collinear).

Two long,straight wires carry equal currents of $10 \ A$ in opposite directions as shown in the figure. The separation between the wires is $5.0 \ cm$. The magnitude of the magnetic field at a point $P$ midway between the wires is . . . . . . $\mu T$. (Given: $\mu_0 = 4\pi \times 10^{-7} \ TmA^{-1}$)