C1 = 600 pF, V1 = 200 V , C2 = 600 pF , V2 = 0
On connecting charged capacitor to uncharged capacitor, the common potential V across the capacitors is
V =

C1V1+C2V2

C1+C2

=

600×10−12×200+0

(600+600)×10−12

or V = 100 V
Energy stored in capacitors before connection is
Ui =

1

2

C1V12 + 0 =

1

2

× 600 × 10−12×2002 or Ui = 12 µJ
and energy stored in capacitors after connection is
Uf =

1

2

(C1+C2)V2 =

1

2

(600 + 600) × 10−12×1002 or Uf = 6 µJ
Hence the energy lost in the process is
Δ = Uf−Ui = (6 - 12) µJ or ΔU = - 6 µJ