A uniform magnetic field B has constant strength b teslas in the z direction i e B 0 0 b a Verify that A B x r is a vector potential for B where r x y 0 b Calculate the flux of B through the rectangle with vertices A B C and D in Figure 17 Flux B A Z B FIGURE 17 A 5 0 2 B 5 2 0 C 0 2 0 D 0 0 2 F 5 0 0