In the given circuit,what are the electric potentials at points $A$ and $B$?

Three identical charged capacitors each of capacitance $5 \,\mu F$ are connected as shown in the figure. The potential difference across capacitor $(3)$,a long time after the switches $K_1$ and $K_2$ are closed,is ............ $V$.

In the given circuit, what are the potential differences between points $A$ and $B$ $(V_{AB})$ and between points $B$ and $C$ $(V_{BC})$?

In the given circuit,if the equivalent capacitance between $A$ and $B$ is $1\,\mu F$,what is the value of $C$?

Two capacitors $C_1 = 2 \mu F$ and $C_2 = 4 \mu F$ are connected in a circuit as shown in the figure. The potential difference $(V_A - V_B)$ is....$V$

There exists a uniform electric field $E = 4 \times 10^5 \, Vm^{-1}$ directed along the negative $x$-axis such that the electric potential at the origin is zero. $A$ charge of $-200 \, \mu C$ is placed at the origin,and a charge of $+200 \, \mu C$ is placed at $(3 \, m, 0)$. The electrostatic potential energy of the system is ........... $J$.