A parallel plate capacitor with air between the plates has a capacitance of 9pF. The separation between its plates is d. The space between the plates is now filled with two dielectrics. One of the dielectrics has dielectric constant k1 = 3 and thickness d/3 while the other one has dielectric constant k2 = 6 and thickness 2d/3. Capacitance of the capacitor is now
(a) 20.25pF
(b) 1.8pF
(c) 45pF
(d) 40.5pF.
