Two conducting shells of radius $a$ and $b$ are connected by conducting wire as shown in figure. The capacity of system is :

The capacity of a parallel plate condenser is $15\,\mu \,F$, when the distance between its plates is $6 \,cm$. If the distance between the plates is reduced to $2\, cm$, then the capacity of this parallel plate condenser will be……$\mu \,F$

The distance between the plates of a charged parallel plate capacitor is $5\  cm$ and electric field inside the plates is $200\  Vcm^{-1}$. An uncharged metal bar of width $2\  cm$ is fully immersed into the capacitor. The length of the metal bar is same as that of plate of capacitor. The voltage across capacitor after the immersion of the bar is……$V$

Two identical charged spherical drops each of capacitance $C$ merge to form a single drop. The resultant capacitance is

Two spherical conductors $A$ and $B$ of radii $a$ and $b$ $(b > a)$ are placed concentrically in air. The two are connected by a copper wire as shown in figure. Then the equivalent capacitance of the system is