A parallel plate capacitor with air as dielectric has a capacitance of $4 \mu \mathrm{~F}$. The space between the plates of the capacitor is completely filled with a material of dielectric constant 5 and charged to a potential of 100 V . The work done to completely remove the dielectric material after the capacitor is disconnected from the battery is

If the rate of change in electric flux between the plates of a capacitor is $9 \pi \times 10^3 \mathrm{Vms}^{-1}$, then the displacement current inside the capacitor is

As shown in the figure, a dielectric of constant $K$ is placed between the plates of a parallel plate capacitor and is charged to a potential $V$ using a battery. If the dielectric is pulled out after disconnecting the battery from the capacitor, the final potential difference across the plates of the capacitor is