A parallel-plate capacitor has capacitance C = 12. 5 pF when the volume between the plates is filled with air. The plates are circular, with radius 3. 00 cm. The capacitor is connected to a battery, and a charge of magnitude 25. 0 pC goes onto each plate. With the capacitor still connected to the battery, a slab of dielectric is inserted between the plates, completely filling the space between the plates. After the dielectric has been inserted, the charge on each plate has magnitude 45. 0 pC. (a) What is the dielectric constant K of the dielectric? (b) What is the potential difference between the plates before and after the dielectric has been inserted? (c) What is the electric field at a point midway between the plates before and after the dielectric has been inserted?