The resultant capacitance between $A$ and $B$ in the fig. is.....$\mu F$

A point charge $'q'$ is placed at a point inside a hollow conducting sphere. Which of the  following electric force pattern is correct ?

Two condensers, one of capacity $C$ and the other of capacity $\frac{C}{2}$ , are connected to a $V\, volt$ battery, as shown. The work done in charging fully both the condensers is

The energy stored in the capacitor is $'U'$. If an uncharged capacitor of same capacity is connected in parallel with it, then energy stored in each capacitor is

Four metallic plates, each with a surface area of one side $A$, are placed at a distance $d$ from each other. The plates are connected as shown in the figure. The capacitance of  the system between $a$ and $b$ is

A parallel plate capacitor has circular plates of $10\, cm$ radius separated by an air-gap of $1\, mm$ . It is charged by connecting the plates to a $100\, volt$ battery. Then the change in energy stored in the capacitor when the plates are moved to a distance of $1\, cm$ and the plates are maintained in connection with the battery, is