A parallel-plate capacitor has an area of 25 cm2, and a separation distance of 3.50 mm. A charge of 25

µC is placed on the capacitor.

(a) Calculate the capacitance of the capacitor, the voltage across the capacitor, and the electric field between the plates.   Show your work below, and record your answers in the boxes provided (don’t forget the units!).

Now, a sheet of plastic 3.50 mm thick is placed between the plates, thereby completely filling the space between them. The dielectric constant of the sheet is κ = 4.0.  The charge on the plates remains the same as in part (a).

(b) With the dielectric inserted, calculate the capacitance, the voltage across the capacitor, and the electric field between the plates.   Show your work below, and record your final answers in the boxes provided (don’t forget the units!).

Now, the dielectric from part (b) is removed, and a new sheet, also with dielectric constant κ = 4.0 but with half the thickness (1.75 mm) is placed inside the capacitor, thereby filling only half the space between the plates, as shown in the figure.  Again, the charge on the plates remains fixed.