Connecting wires carrying currents in opposite directions are twisted together in electrical appliances in order to reduce:

$\frac{V \cdot s}{A \cdot m}$ is the unit of which physical quantity?

Two wires $A$ and $B$ are of lengths $40 \ cm$ and $30 \ cm$. $A$ is bent into a circle of radius $r$ and $B$ into an arc of radius $r$. $A$ current $i_1$ is passed through $A$ and $i_2$ through $B$. To have the same magnetic inductions at the centre, the ratio of $i_1: i_2$ is

Two concentric and coplanar rings of radius $r$ and $R$ are shown in the figure. Find the magnetic flux linked through the smaller coil when the same current $I$ flows through each in opposite directions $(r << R)$.

The correct Biot-Savart law in vector form is

The magnetic field at the centre $C$ of the arrangement shown in the figure is: