Worked example: A 10 μF capacitor is charged to 100 V, then disconnected and connected to an uncharged 10 μF capacitor. Find the initial energy, final energy, and energy lost. Step 1: Initial U_i = (1/2)CV² = 0.5 × 10⁻⁵ × 10⁴ = 0.05 J. Charge Q = CV = 10⁻³ C = 1 mC. Step 2: Connected, charge shares equally (identical C): each gets 0.5 mC, common voltage V' = Q_total/Ceq_parallel = 10⁻³/(2 × 10⁻⁵) = 50 V. Step 3: Final U_f = (1/2)(2 × 10⁻⁵)(50)² = 0.025 J. Step 4: Energy lost = 0.05 − 0.025 = 0.025 J — exactly half, dissipated as heat/spark/radiation in the wires. Charge was conserved (1 mC before and after); energy was not. This is the classic result: connecting identical capacitors wastes half the energy.