A long metal pipe of square cross-section (side a) is grounded on three sides, while the fourth (which is insulated from the rest) is maintained at constant potential Vo. Find the net charge per unit lenght on the side opposite to Vo. A long metal pipe of circular cross-section (radius R) is divided (lenghtwise) into four equal sections, three of them grounded and the fourth maintained at constant potential V0. Find the net charge per unit lenght on the side opposite to V0.