Three identical capacitors of capacitance $C$ each are connected in series and this connection is connected in parallel with one more such identical capacitor. The equivalent capacitance of the whole combination is:

Three long concentric conducting cylindrical shells have radii $R$,$2R$,and $2\sqrt{2}R$. The inner and outer shells are connected to each other. The capacitance across the middle and inner shells per unit length is:

Four capacitors are connected as shown in the figure. If $C_1, C_2, C_3$ and $C_4$ are in the ratio of $1: 2: 3: 4$,then the ratio of the charges on the capacitors $C_2$ and $C_4$ is

Find the equivalent capacitance between $A$ and $B$.

Find the equivalent capacitance between $A$ and $B$ of the following arrangement:

Two capacitors of capacities $2 \mu F$ and $4 \mu F$ are connected in parallel. $A$ third capacitor of $6 \mu F$ capacity is connected in series with this combination. $A$ battery of $12 \text{ V}$ is connected across this combination. The charge on the $2 \mu F$ capacitor is: (in $\mu C$)