Biot-Savart's Law

What is a current element?

The direction of the magnetic field at a point P above the wire carrying currents shown in the figure is

A current is flowing north along a power line. The direction of the magnetic field above it, neglecting the earth's field, is towards,

Equal currents $i$ flow in two wires along $\mathrm{x} \mathrm{and} \mathrm{y}-\mathrm{axis}$ as shown. Match the following.
                 
 

Two infinitely long, thin, insulated straight wires lie in the $\mathrm{x}-\mathrm{y}$ plane along the $\mathrm{x}$ and $\mathrm{y}$-axes respectively. Each wire carries a current $\mathrm{I}$, respectively in the positive $\mathrm{x}$-direction and the positive $\mathrm{y}$-direction. Find the locus of a point in this plane where the magnetic field is zero.

Magnetic field at the centre (at nucleus) of hydrogen like atoms (atomic number $=Z$) due to motion of electron in $n^{\mathrm{th}}$ orbit is proportional to