Two circular coils $P$ and $Q$ are made from two identical wires of the same length. The number of turns in coils $P$ and $Q$ are $4$ and $2$,respectively. The magnetic inductions at the centers of $P$ and $Q$ are $B_P$ and $B_Q$,respectively. The ratio $\frac{B_P}{B_Q}$ is

In the following figure,the magnitude of the magnetic field at the point $P$ is:

$20 \, A$ current is flowing in a long straight wire. The intensity of the magnetic field at a distance of $20 \, cm$ from the wire will be:

$A$ circular coil of radius $R$ is carrying a current $I_{1}$ in an anticlockwise sense. $A$ long straight wire is carrying a current $I_{2}$ in the negative direction of the $x$-axis. Both are placed in the same plane and the distance between the centre of the coil and the straight wire is $d$. The magnetic field at the centre of the coil will be zero for the value of $d$ equal to:

The source of magnetic field is . . . . . . and source of electric field 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