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 $\text{ Wb m}^{-2}$)

$A$ steady current is set up in a cubic network composed of wires of equal resistance and length $d$ as shown in the figure. What is the magnetic field at the centre $P$ due to the cubic network?

In the following figure, the magnitude of the magnetic field at point '$O$' will be

$A$ square frame of side $l$ carries a current $i$. The magnetic field at its centre is $B$. The same current is passed through a circular coil having the same perimeter as the square. The field at the centre of the circular coil is $B^{\prime}$. The ratio of $\frac{B}{B^{\prime}}$ is

Which of the following graphs represents the magnetic field $(B)$ versus distance $(r)$ from the centre of a long straight conducting wire of uniform cross-sectional area carrying a steady current $I$ and having radius $a$?

The magnetic field at the centre $O$ due to the given structure is: