Question

Consider two 100𝜇𝐹 capacitors. One is charged to10V, disconnected from the power supply, and then connected across the other. Calculate the energy stored by the combination 

Answer 1

$W=\frac{C_0 U_0^2}{2},$$C_0=C_1+C_2=2C,$

$U_0=U_1=U_2=U,$

$W=CU^2,$

$W=100\cdot 10^{-6}\cdot 10^2=0.01~J.$