The Biot-Savart law states that the magnetic field dB at a point P due to a small current element Idl is given by:
$$
dB = \frac{\mu_0}{4\pi} \frac{I(dl \times r)}{r^3}
$$
where $\mu_0$ is the permeability of free space, $I$ is the current, $dl$ is the small
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