According to Biot-Savart law, the magnitude of the field in SI unit is given by:
1
dB = \({\mu_0 \ I \ dl sin\theta \over 4\pi\ {r^{2}}} \)
2
dB = \({\mu_0\ I\ dl sin\theta \over 4\pi\ {r}} \)
3
dB = \({4\pi\ \mu_0\ I\ dl sin\theta \over {r^{2}}} \)
4
dB = \({4\pi\ \mu_0\ I\ dl sin\theta \over r} \)