A parallel plate capacitor is an arrangement of two identical metal plates kept parallel, a small distance apart. The capacitance of a capacitor depends on the size and separation of the two plates and also on the dielectric constant of the medium between the plates. Like resistors, capacitors can also be arranged in series or parallel or a combination of both. By virtue of electric field between the plates, charged capacitors store energy. (a) The capacitance of a parallel plate capacitor increases from $10\text{ }\mu\text{F}$ to $80\text{ }\mu\text{F}$ on introducing a dielectric medium between the plates. Find the dielectric constant of the medium. (b) $n$ capacitors, each of capacitance $C$, are connected in series. Find the equivalent capacitance of the combination. (c) A capacitor is charged to a potential ($V$) by connecting it to a battery. After some time, the battery is disconnected and a dielectric is introduced between the plates. How will the potential difference between the plates, and the energy stored in it be affected ? Justify your answer.