Electrical Engineering ⇒ Topic : Force Between Current-Carrying Parallel Conductors

Force Between Current-Carrying Parallel Conductors

When two current-carrying conductors are parallel to each other, a mechanical force acts on each of the conductors. This force is the result of each conductor being acted upon by the magnetic field produced by the other. If the currents are in the same direction, the forces are attractive ; if currents are in opposite direction, the forces are repulsive. This can be beautifully illustrated by drawing the magnetic field produced by each conductor.

Currents in the same direction. Consider two parallel conductors A and B carrying currents in the same direction (i. e. into the plane of paper) as shown in Fig. a (i) . Each conductor will set up its own magnetic field as shown. It is clear that in the space between A and B, the two fields are in opposition and hence they tend to cancel each other. However, in the space outside A and B, the two fields assist each other. Hence the resultant field distribution will be as shown in Fig. a (ii).

                                                                        figure (a)

Since magnetic lines of force behave as stretched elastic cords, the two conductors are attracted towards each other. Alternatively, the conductors can be viewed as moving away from the relatively strong field (in the space outside A and B) into the weaker field between the conductors.

Currents in opposite direction. Consider two parallel conductors A and B carrying currents in the opposite direction as shown in Fig (a). Each conductor will set up its own field as shown. It is clear that in the space outside A and B, the two fields are in opposition and hence they tend to cancel each other. However in the space between A and B, the two fields assist each other. The lateral pressure between lines of force exerts a force on the conductors tending to push them apart. In other words, the conductors experience a repulsive force.

          If currents are in the same directions, the conductors attract each other ; if currents are in opposite directions, the conductors repel each other

                                                                   figure (a)