4. A rectangular thin-wire loop shown in Fig. 4 has given dimensions a x b and total resistance R. This loop is being moved with constant speed along the x-axis direction parallel to its a-side. This spatial region features magnetic field B that is perpendicular to the page everywhere but is spatially nonuniform: its magnitude B(x) Bo+x varies linearly with coordinate x with known parameters Bo and B. How much Joule heat (energy) W will be dissipated in the loop during the displacement of its left edge from "old" position x1 (loop displayed in black color) to "new" position 2 (displayed in red color)? B(x) b x1 X2 a Figure 4: Illustration for problem 4.