Which of the following graphs represents the magnetic field $(B)$ versus distance $(r)$ from the centre of a long straight conducting wire of uniform cross-sectional area carrying a steady current $I$ and having radius $a$?

Two mutually perpendicular conductors carrying currents $I_1$ and $I_2$ lie in one plane. The locus of the point at which the magnetic induction is zero,is a

$PQRS$ is a square loop made of uniform conducting wire. If the current enters the loop at $P$ and leaves at $S$, then the magnetic field will be

The magnetic field $d\overrightarrow{B}$ due to a small current element $d\overrightarrow{l}$ at a distance $\overrightarrow{r}$ from an element carrying current $i$ is given by:

$A$ circular loop and an infinitely long straight conductor carry equal currents,as shown in the figure. The net magnetic field at the centre of the loop is $B_1$,when the current in the loop is clockwise and $B_2$ when the current in the loop is anti-clockwise. Then $\frac{B_1}{B_2}$ is

$A$ square frame of side $1 \ m$ carrying a current $I$ produces a magnetic field $B$ at its centre. The same current is passed through a circular coil having the same perimeter as the square. The magnetic field at the centre of the circular coil is $B^{\prime}$. The ratio of $\frac{B}{B^{\prime}}$ is