Force Between Two Parallel Current-Carrying Conductors
The force on a length l of each of two long, straight, parallel wires carrying currents i1 and i2 and separated by a distance a is (Fig. 27)
Hence, force per unit length,
Direction of force
If a number of conductors carry current in the same direction, then the force between them will be attractive. If the conductors carry current in the opposite direction, then the force between them will be repulsive (Fig. 28).