An electrician requires a capacitance of $6\mu \mathrm{F}$ in a circuit across a potential difference of $1.5\mathrm{kV}$. A large number of $2\mu \mathrm{F}$ capacitors which can withstand a potential difference of not more than $500 \mathrm{V}$ are available. The minimum number of capacitors required for the purpose is

The equivalent capacitance between $A$ and $B$ is,

For the arrangement of capacitors as shown in the circuit, the effective capacitance between point $A$ and $B$ is (capacitance of each capacitor is $4\mu F)$

In figure, charge on the capacitor is plotted against potential difference across the capacitor. The capacitance and energy stored in the capacitor are respectively.