If the charge on the capacitor is increased by $3 \ C$,the energy stored in it increases by $21 \%$. The original charge on the capacitor is (in $C$)

$A$ cylindrical capacitor has charge $Q$ and length $L$. If both the length and the charge are doubled (keeping other parameters constant),the energy stored in the capacitor will:

For a capacitor with area $A$ and potential difference $V$ separated by a distance $d$,the energy per unit volume is:

If the charge on a body is increased by $2 \ C$,the energy stored in it increases by $21 \%$. The original charge on the body in coulomb 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.

$A$ capacitor of capacitance $C$ is fully charged. It is discharged through a small coil of negligible resistance embedded in a thermally insulated block of mass $m$ and specific heat capacity $S$. If the temperature of the block rises by $\Delta T$,find the potential difference across the capacitor.