Physics · Ch 3 — Magnetism and Magnetic Effects of Electric Current
Force Between Two Long Parallel Current Carrying Conductors
Force Between Two Long Parallel Current Carrying Conductors
Two long straight parallel wires A and B, separated by distance , carry currents and . Wire A produces, at the location of wire B, a field (§3.8.2); the force this exerts on a length of wire B (from §3.10.5, ) works out, per unit length, to
Working through the direction carefully (using the right-hand rule for and Fleming's left-hand rule for the resulting force) shows that when the two currents flow in the same direction, the force is attractive; when they flow in opposite directions, the force is repulsive -- the same magnitude of force acts symmetrically back on wire A due to wire B's field, by Newton's third law.
This force is used to define the ampere itself: …
What this figure shows. Two long straight wires A and B run parallel to each other, separated by distance r, carrying currents I1 and I2 respectively along the same (z) direction. The field B1 produced by wire A at the location of wire B is drawn, directed into the page there by the right- …
What this figure shows. Two parallel wires, both carrying current in the same direction, are drawn with a force arrow on each pointing toward the other wire -- illustrating that like-directed parallel currents attract, exactly the way each wire's own circular field lines pull the neighbouring wire's current element in toward it. …
What this figure shows. Two parallel wires, carrying current in opposite directions, are drawn with a force arrow on each pointing away from the other wire -- illustrating that oppositely-directed parallel currents repel, the mirror-image case of Figure 3.55 obtained simply by reversing the direction of one of the two currents. …