A capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of resulting system

When the capacitor is charged by a battery of potential V, then energy stored in the capacitor,Ui=12CV2                   . . . . (i) When the battery is removed and another  identical  uncharged capacitor is connected in parallel Common potential,V'=CVC+C=V2∴ Then the energy stored in the capacitor, Uf=12(2C)V22=14CV2                        . . . . (ii)∴ From eqns. (i) and (ii) Uf=Ui2that means the total electrostatic energy of resulting system will decreases by a factor of 2.