A long cylindrical conductor of radius R carries a current I, as shown shown in the figure. The current density is uniform over the section conductor cross section. A correct expression for the field magnetic B, due to this current I, at a distance r2 > R measured from the center of the conductor, it is: HOIR a) 2nr2 b) Hobr? 3 c) HobR3 3r2 d) Hol 2tr2