A capacitor stores 10 µC charge when connected across a battery. When the gap between the plates is filled with a dielectric, a charge of 20 µC flows through the battery. Find the dielectric constant of the dielectric.

k = 3

In absence of dielectric

Q = CV = 10 µC                 . . . (1)

With dielectric

Q' = kCV = 30 µC               . . . (2)

From (i) and (2)

k = 3