Two isolated charged metallic spheres of radii $R_1$ and $R_2$ having charges $Q_1$ and $Q_2$, respectively, are connected to each other, then there is:

 

A parallel plate capacitor of capacitance $C$ is as shown. A thin metal plate $A$ is placed between the plates of the given capacitor in such a way that its edges touch the two plates as shown. The capacity a cross $P$ and $Q$now becomes

The energy stored in a capacitor is in the form of

If $E$ is the electric field intensity of an electrostatic field, then the electrostatic energy density is proportional to,