To characterize the forces that magnetic fields exert on current-carrying conductors we introduce a vector quantity - the magnetic fieldB. The vector of magnetic field B can be determined by the magnetic force that acts on a straight conductor with length l carrying the current I. If the conductor is at an angle α to the vector B, a force of magnitude F = Iblsinα acts on it. The direction of the vector of force F is consistent with the direction of the current and the vector of field B, in accordance with the right-hand rule. Magnetic field lines are tangent to the magnetic field vector B at any given point. The magnetic field lines of a straight conductor are depicted as circles around the conductor, and are situated in the planes that are perpendicular to it. In SI, the magnetic field at the distance r from a straight conductor that carries the current I is expressed by the following formula:

B = (μ_{0}I)/(2πr) ,

Where μ_{0} = 4π*10^{-7} N/A^{2} is magnetic constant.

The magnetic field of a straight conductor is inversely proportional to the first power of the distance r from the conductor.