A parallel plate capacitor of capacitance $C$ is connected to a battery and is charged to a potential difference $V$. Another capacitor of capacitance $2C$ is connected to another battery and is charged to potential difference $2V$. The charging batteries are now disconnected and the capacitors are connected in parallel to each other in such a way that the positive terminal of one is connected to the negative terminal of the other. The final energy of the configuration is

$N$ identical capacitors are joined in parallel and the combination is charged to a potential $V$. Now if they are separated and then joined in series then the energy of combination will

Two parallel plate capacitors whose capacities are$C$ and $2C$ respectively, are joined in parallel. These are charged by $V$ potential difference. If the battery is now removed and a dielectric of dielectric constant $K$ is filled in between the plates of the capacitor $C$, then, what will be the potential difference across each capacitor?