Discuss special cases of the Biot-Savart law.

(N/A) $(1)$ If $\theta = 0^{\circ}$,then $\sin 0^{\circ} = 0$,which implies $dB = 0$. This means the magnetic field is zero at points located on the axis of the current element.
$(2)$ If $\theta = 90^{\circ}$,then $\sin 90^{\circ} = 1$,which implies $dB$ is maximum. This means the magnetic field due to a current element is maximum in a plane passing through the element and perpendicular to its axis.