The current is flowing in the south direction along a power line. The direction of the magnetic field above the power line (neglecting the Earth's field) is

$A$ single current-carrying loop of wire with current $I$ flowing in an anticlockwise direction when seen from the $+ve\;z$ direction,lying in the $xy$ plane,is shown in the figure. The plot of the $\hat{j}$ component of the magnetic field $(B_y)$ at a distance $a$ (less than the radius of the coil) on the $yz$ plane versus the $z$ coordinate looks like:

Three rings,each having equal radius $R$,are placed mutually perpendicular to each other,and each has its centre at the origin of the coordinate system. If current $I$ is flowing through each ring,then the magnitude of the magnetic field at the common centre is

In the following figure,a wire bent in the form of a regular polygon of $n$ sides is inscribed in a circle of radius $a$. The net magnetic field at the centre will be

In a hydrogen atom, an electron is revolving in an orbit of radius $0.53 \, \text{\AA}$ with $6.6 \times 10^{15} \, \text{rotations/second}$. The magnetic field produced at the centre of the orbit is ....... $Wb/m^2$.

$A$ moving charge can produce which field? Explain.