For the given circuit, at time $t=0,$ the initial voltage across $10F,20F,30F,40F$ and $50F$ capacitors are $10V,0V,20V,0V$ and $0$ V respectively. Switch $S_1,S_2,S_3$ and $S_4$ operates simultaneously. When $S_1$ and $S_4$ are closed, terminals A and B are connected; when they are opened, terminals A and B are disconnected. Similarly, when $S_3$ and $S_4$ are closed, terminals C and D are connected; when they are opened, terminals C and D are disconnected. Assume that switches $S_2$ and $S_3$ have been closed $($connecting terminals C and D $)$ for a long period of time. At $t=T_1,$ switches $S_1$ and $S_4$ are closed, and $S_2$ and $S_3$ are opened for a long period.