The previous example is very important. If gives a way to look at the force between two current carrying wires.

Notice that the equation does not calclate the force directly, but the force per unit length. Its units are, ^N/_m. To determine oif the current carrying wires are attracted or repelled, use Ampere's Law,(the closed right hand rule.) If the b-fields between the currents point in the same direction, then the wires are repelled. If the b-fields in between the wires point in opposite directions, then the wires are attracted. See the example below.