We consider two long straight parallel wires separated by a distance d carrying currents I1 and I2 . Let us examine the case where the two currents are in the same direction, as in Figure given below.
Wire 2 will experience a magnetic field of due to wire 1 in the direction indicated, and hence will experience a force.
The direction of F2 indicated shows that wire 2 will be attracted towards wire 1. In a similar manner, we can show that wire 1 will experience a force due to the magnetic field B2 of wire 2, and that this force F1 will have a magnitude equal to that of F2 but opposite in direction.Thus, wire 1 will be attracted towards wire 2.