Ampere's law

Ampere's law (ampere's swimming law)

Law of electromagnetism that describes mathematically the magnetic force between two electric currents.

It was named after A.-M. Ampère, who discovered that such forces exist. If two currents flow in the same direction, the force between the two wires is attractive; if they flow in opposite directions, the force is repulsive. In each case, the force is directly proportional to the currents.

source:Britannica encyclopedia