The magnetic effect of current was discovered by

In the current-carrying conductor $(AOCDEFG)$ as shown,the magnetic induction at the point $O$ is ($R_1$ and $R_2$ are radii of arcs $CD$ and $EF$ respectively,$I$ = current in the loop,$\mu_0$ = permeability of free space).

$A$ cell is connected between the points $A$ and $C$ of a circular conductor $ABCD$ of center $O$ with angle $AOC = 60^o$. If $B_1$ and $B_2$ are the magnitudes of the magnetic fields at $O$ due to the currents in $ABC$ and $ADC$ respectively,the ratio $B_1/B_2$ is

An infinitely long straight conductor is bent into the shape as shown below. It carries a current of $I$ ampere and the radius of the circular loop is $R$ metre. Then, the magnitude of magnetic induction at the centre of the circular loop is

Consider two infinitely long wires parallel to the $Z$-axis carrying the same current $I$ in the positive $Z$-direction. One wire passes through point $L$ at coordinates $(-1, 1)$ and the other wire passes through point $M$ at coordinates $(-1, -1)$. The resultant magnetic field at the origin $O$ will be

$Weber/m^2$ is equal to