"40 In Fig. 2957, four long straight wires are perpendicular to the page, and their cross sections form a square of edge length a = 8.50 cm. Each wire carries 15.0 A, and all the currents are out of the page. In unitvector notation, what is the net magnetic force per meter of wire length on wire 1? to? #64196 Figure 29-57 Problems 29, 37, and 40