If an electron revolves around a nucleus in a circular orbit of radius $R$ with frequency $n$,then the magnetic field produced at the centre of the nucleus will be

Equal currents $I$ are flowing in three infinitely long wires along the positive $x$,$y$,and $z$ directions. The magnetic field at a point $(0, 0, -a)$ would be:

In the figure shown,there are two semicircles of radii $r_1$ and $r_2$ in which a current $i$ is flowing. The magnetic induction at the centre $O$ will be

$A$ circular loop of a wire and a long straight wire carry currents $I_c$ and $I_e$,respectively,as shown in the figure. Assuming that these are placed in the same plane,the magnetic field will be zero at the centre of the loop when the separation $H$ is:

$A$ current $I$ is flowing along an infinite,straight wire in the positive $Z$-direction,and the same current $I$ is flowing along a similar parallel wire $5 \ m$ apart in the negative $Z$-direction. $A$ point $P$ is at a perpendicular distance of $3 \ m$ from the first wire and $4 \ m$ from the second. What is the magnitude of the magnetic field $B$ at point $P$?

Two identical circular wires of radius $20\,cm$ and carrying current $\sqrt{2}\,A$ are placed in perpendicular planes as shown in the figure. The net magnetic field at the centre of the circular wires is $.............\times 10^{-8}\,T$. (Take $\pi=3.14$ )