Force between Parallel Conductors

Two wires carrying current in the vicinity of one another exert a force on each other because of their magnetic fields. An end view of two conductors is shown in the following figure.

FIGURE

In part A, electron flow in both conductors is toward the reader, and the magnetic fields are anticlockwise around the conductors between the wires. In this case, the fields cancel because the directions of the two fields oppose each other. The wires are forced in the direction of the weaker field, toward each other. This force is one of attraction.

In part B, the electron flow in the two wires is in opposite directions. Therefore, the magnetic fields are clockwise in one and anticlockwise in the other, as shown. The fields reinforce each other between the wires and the wires are forced in the direction of the weaker field, away from each other. This force is one of repulsion.

To summarize: Conductors carrying current in the same direction tend to be drawn together; conductors carrying current in opposite directions tend to be repelled from each other.