Question

Consider two 100microfarads capacitors.one charged to 10 V, disconnected from power supply and then connected across the other.calculate the energy stored by the combination

Answer 1

$$q=CU\\C'=2C\\ E=0.5\frac{q^2}{2C'}\\ E=0.5\frac{C^2U^2}{4C}\\ E=\frac{CU^2}{8}\\ E=\frac{(10^{-4})(10)^2}{8}=1.25\ mJ$$