Along cylindrical conductor carries current in one direction uniformly spread over the cross section. (i. e. j is directed parallel to the axis and is constant). a very thin layer of insulation surrounds the cylinder, which in turn is surrounded by a very thin cylindrical shell which shares its axis of symmetry with the inner cylinder. the current returns in the outer cylindrical shell. (a) find the energy stored in a length l of this composite cable. (b) find the self-inductance of this cable per unit length.