In each of the 10 cases below, 2 - 4 Very long straight wires are parallel to each other. Rank the strength of the total magnetic force on each of the labeled wires. So each case has 2-4 wires with varying currents and distances between; I have to calculate the magnetic force and then rank all of the wires by magnitude. For example, the 1st one looks like: Wire A: ----->-----3A Wire B: ----->-----2A Wire C: ----->-----6A Distance from Wire A to Wire B = d Distance from Wire B to Wire C = 2d (and from A to C is 3d obviously). Using Ampere's Law, I calculated Wire A's magnitude to be 12A/d, which is correct. I found Wire B = -12A/d which is wrong, the correct answer is 0. Apparently the force vectors cancel out but I thought they should be added. Can someone explain?