We know that work done by magnetic force is always 0. So we put a wire in horizontal plane in which current flows from west to east. Magnetic field here is inside the paper(due to current) .A rod is placed over the wire in the same horizontal plane. L is the separation distance between the two. The rod will experience a magnetic force in upward direction. The L distance is also taken in upward direction. So work done (f.l) should be positive. But its not.How???