Biot-Savart law
A current which flows to a wire, causes a magnetic field in the neighbourhood of the wire. If the current is of constant magnitude, the Biot-Savart law can be used to calculate the magnitude and direction of the magnetic field. Biot-Savart law

The Biot-Savart law is derived from the formula which we use to calculate the magnetic field caused by a point charge. This formula is as follows: Magnetic field point charge If qv is replaced by Idl, one can calculate the contribution to the magnetic field caused by an infinitesimal particle. By integrating this along the length of the wire it is possible to calculate the total magnetic field in a certain point.