The mean electric energy density between the plates of a charged capacitor is (here $q$ = charge on the capacitor and $A$ = area of the capacitor plate).

Three identical capacitors are combined in different ways. For the same voltage applied to each combination,the one that stores the greatest energy is:

If the distance between the plates of a capacitor with capacitance $C$ and charge $Q$ is doubled,the work done is:

The plates of a parallel plate capacitor have an area of $90 \,cm^{2}$ each and are separated by $2.5 \,mm$. The capacitor is charged by connecting it to a $400 \,V$ supply.
$(a)$ How much electrostatic energy is stored by the capacitor?
$(b)$ View this energy as stored in the electrostatic field between the plates,and obtain the energy per unit volume $u$. Hence arrive at a relation between $u$ and the magnitude of electric field $E$ between the plates.

If the charge on the capacitor is increased by $3 \ C$,the energy stored in it increases by $44 \%$. The original charge on the capacitor is (in $C$)

$A$ parallel plate capacitor of capacitance $1 \ \mu F$ is charged to a potential difference of $20 \ V$. The distance between the plates is $1 \ \mu m$. The energy density between the plates of the capacitor is: