Energy is stored in what form in a capacitor?

$A$ capacitor has two circular plates,each of radius $8\,cm$,separated by a distance of $1\,mm$. $A$ dielectric slab (dielectric constant $K = 6$) is inserted between the plates. Calculate the energy stored in the capacitor when it is connected to a $150\,V$ potential difference.

$A$ capacitor is charged by a battery and the energy stored in it is $U$. The battery is now removed and the separation distance between the plates is doubled. The energy stored now is:

An air-filled parallel plate capacitor has a uniform electric field $E$ in the space between the plates. If the distance between the plates is $d$ and the area of each plate is $A$,the energy stored in the capacitor is ($\epsilon_{0} =$ permittivity of free space).

$A$ capacitor having a capacity of $2.0 \; \mu F$ is charged to $200 \; V$ and then the plates of the capacitor are connected to a resistance wire. The heat produced in joules will be:

The area of a cloud is $25 \times 10^6\ m^2$ and the electric potential is $10^5\ V$. If the height of the cloud is $0.75\ km$, then the energy stored between the cloud and the earth is.....$J$