Two spherical conductors $A_1$ and $A_2$ of radii $r_1$ and $r_2$ are placed concentrically in the air. The two are connected by a copper wire as shown in the figure. Then the equivalent capacitance of the system is

There are two conducting spheres of radius $a$ and $b$ $(b>a)$ carrying equal and opposite charges. They are placed at a separation $d(>>>a\mathit{ }\mathit{\&} b).$ The capacitance of the system is

A network of uncharged capacitors and resistances is as shown.

Current through the battery immediately after the key, $K$ is closed and after a long time interval is:

Six capacitors each of capacitance $C$ is connected as shown in the figure and initially all the capacitors are uncharged. Now a battery of $\mathrm{emf} =\mathrm{\epsilon }$ is connected. How much charge will flow through the battery if the switch is on?

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

$C_1=3 \mathrm{\mu F}, C_2=6 \mathrm{\mu F} \mathrm{and} C_3=2 \mathrm{\mu F}$, then equivalent capacitance between $a$ and $b$ is