P.6-15 In certain experiments it is desirable to have a region of constant magnetic flux density. This can be created in an off-center cylindrical cavity that is cut in a very long cylindrical conductor carrying a uniform current density. Refer to the cross section in 10 y 0 FIGURE 6-40 Cross section of a long cylindrical conductor with cavity (Problem P.6-15). Fig. 6-40. The uniform axial current density is J = a.J. Find the magnitude and direction of B in the cylindrical cavity whose axis is displaced from that of the conducting part by a distance d. (Hint: Use principle of superposition and consider B in the cavity as that due to two long cylindrical conductors with radii b and a and current densities J and -J, respectively.)