In figure two parallel infinitely long current carrying wires are shown. If resultant magnetic field at point $A$ is zero. Then determine current $I.$ (in $A$)

An electron is revolving round a proton, producing a magnetic field of $16\, weber/m^2$ in a circular orbit of radius $1\,\mathop A\limits^o $. It’s angular velocity will be

A current loop consists of two identical semicircular parts each of radius $R,$ one lying in the $x-y$ plane and the other in $x-z$ plane. If the current in the loop is $i.$ The resultant magnetic field due to the two semicircular parts at their common centre is

In an ionised sodium atom, an electron is moving in a circular path of radius $r$ with angular velocity $\omega $. The magnetic induction in $wb/m^2$ produced at the nucleus will be

A coil carrying a heavy current and having large number of turns mounted in a $N-S$ vertical plane and $a$ current flows in clockwise direction. A small magnetic needle at its cente will have its north pole in

The magnetic field on the axis of a circular loop of radius $100\,cm$ carrying current $I=\sqrt{2}\,A$, at point $1\,m$ away from the centre of the loop is given by