A parallel$-$plate capacitor of capacitance C$0$C$0$ has plates of area AA with separation dd$.$ Initially the gap between the plates is filled with air. The capacitor is connected to a battery with voltage V$0$V$0,$ the capacitor reaches its full charge, and then the battery is disconnected. A slab of dielectric material with a dielectric constant of $4\mathrm{.}04\mathrm{.}0$ is then inserted into the capacitor, completely filling the region between the plates.