Correct Answer - `(2piKl(T_(2)-T_(1)))/(In(R_(2)//R_(1)))`

Let an element which is hollow cyl. of Radius and width dr

`dR = (dr)/(K2pirl) R = (1)/(2piKl) underset(R_(1))overset(R_(2))int (dr)/(r ) = (1)/(2piKl)`

`(In r)_(R_(1))^(R_(2)) = (1)/(2piKl)In ((R_(2))/(R_(1)))`

`i_(H) = (T_(2)-T_(1))/((1)/(2piKl)ln(R_(2)//R_(1))) =(2piKl(T_(2)-T_(1)))/(ln(R_(2)//R_(1)))`