The equivalent capacitance between points $a$ and $b$ in the given circuit is ........ $\mu F$.

Four identical metal plates are arranged in air at equal distances from each other as shown in the figure. Each plate has an area $A$. Find the equivalent capacitance of the system between points $A$ and $B$.

Eight capacitors,each of capacitance $C$,are connected as shown in the figure. The effective capacitance between $A$ and $B$ is

$A$ parallel combination of two capacitors of capacities $2C$ and $C$ is connected across a $5 \text{ V}$ battery. When they are fully charged,the charges and energies stored in them are $Q_1, Q_2$ and $E_1, E_2$ respectively. Then $\frac{E_1-E_2}{Q_1-Q_2}$ in $\text{J/C}$ is (capacity is in Farad,charge in Coulomb and energy in $\text{J}$)

$A$ capacitor of capacitance $C_1 = 1\ \mu F$ can withstand a maximum voltage $V_1 = 6\ kV$ and another capacitor of capacitance $C_2 = 3\ \mu F$ can withstand a maximum voltage $V_2 = 4\ kV$. When the two capacitors are connected in series,the combined system can withstand a maximum voltage of......$kV$.

Four plates of equal area $A$ are separated by equal distances $d$ and are arranged as shown in the figure. The equivalent capacity is