Write proportionality constant of Biot-Savart law with unit and value (magnitude).

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 wire carrying current $I$ has the shape as shown in adjoining figure.Linear parts of the wire are very long and parallel to $X-$axis while semicircular portion of radius $R$ is lying in $Y-Z$ plane. Magnetic field at point $O$ is

Two circular coils $X$ and $Y$, having equal number of turns, carry equal currents in the same sence and subtend same solid angle at point $O$. If the smaller coil $X$ is midway between $O$ and $Y$, and If we represent the magnetic induction due to bigger coil $Y$ at $O$ as $B_Y$ and that due to smaller coil $X$ at $O$ as $B_X$, then $\frac{{{B_Y}}}{{{B_X}}}$ is

A current of $10\,A$ is passing through a long wire which has semicircular loop of the radius $20\,cm$ as shown in the figure. Magnetic field produced at the centre of the loop is

The magnetic induction at the centre $O$ of the current carrying bent wire shown in the adjoining figure is