Two charges 7 μC and -2 μC are placed at (-9 cm, 0, 0) and (9 cm, 0, 0) respectively in an external electric field E = Ar2 r̂, where A = 9 × 105 N/C·m2. Considering the potential at infinity is 0, the total electrostatic energy of the configuration is ______ J.

Two capacitors C1 and C2 are charged to 100 V and 120 V respectively. When connected together in parallel with opposite polarity plates joined together, the net common potential is found to be zero. Therefore, which relation holds true?

Point charges -3Q, -q, 2q, and 2Q are placed, one at each corner of a square. The relation between Q and q for which the electric potential at the centre of the square is zero is: