Identify the correct statement.

$A$ long curved conductor carries a current $I$. $A$ small current element of length $dl$ on the wire induces a magnetic field at a point away from the current element. If the position vector between the current element and the point is $\vec{r}$,making an angle $\theta$ with the current element,then the induced magnetic field density $d\vec{B}$ at the point is $(\mu_0 = \text{permeability of free space})$:

$A$ single current-carrying loop of wire with current $I$ flowing in an anticlockwise direction when seen from the $+ve\;z$ direction,lying in the $xy$ plane,is shown in the figure. The plot of the $\hat{j}$ component of the magnetic field $(B_y)$ at a distance $a$ (less than the radius of the coil) on the $yz$ plane versus the $z$ coordinate looks like:

Give the differences between Biot-Savart law and Coulomb's law.

Two parallel conducting wires of equal length are placed distance $d$ apart and carry currents $I_1$ and $I_2$ respectively in opposite directions. The resultant magnetic field at the midpoint of the distance between both the wires is

$A$ circular coil of radius '$r$' and number of turns '$n$' carries a current '$I$'. The magnetic fields at a small distance '$h$' along the axis of the coil $(B_a)$ and at the centre of the coil $(B_c)$ are measured. The relation between $B_c$ and $B_a$ is