The energy of a charged capacitor is given by the expression ($q$ = charge on the conductor and $C$ = its capacity).

The mean electrical energy density between the plates of a charged air capacitor is (where $q=$ charge on capacitor,$A=$ area of capacitor plate):

When an additional charge of $2 \text{ C}$ is given to a capacitor,the energy stored in it increases by $21 \%$. The original charge of the capacitor is: (in $\text{ C}$)

The charge $q$ on a capacitor varies with voltage $V$ as shown in the figure. The area of the triangle $AOB$ is proportional to

The energy required to charge a parallel plate capacitor with plate separation $d$ and plate area $A$ such that the uniform electric field between the plates is $E$,is

$A$ parallel plate capacitor has plate area $A$ and separation between plates is $d$. It is charged to a potential difference of $V_0$ volt. The charging battery is then disconnected and plates are pulled apart to three times the initial distance. The work done to increase the distance between the plates is $(\varepsilon_0 = \text{permittivity of free space})$