State the Biot-Savart law.

(N/A) The Biot-Savart law states that the magnetic field $dB$ at a point due to a small current element $Idl$ is given by:
$dB = \frac{\mu_0}{4\pi} \frac{I (dl \times r)}{r^3} = \frac{\mu_0}{4\pi} \frac{I dl \sin\theta}{r^2}$
Where:
- $dB$ is the infinitesimal magnetic field.
- $\mu_0$ is the permeability of free space.
- $I$ is the current flowing through the conductor.
- $dl$ is the length of the current element.
- $r$ is the position vector from the element to the point.
- $\theta$ is the angle between the current element $dl$ and the position vector $r$.