A parallel plate condenser with plate area A and separation d is filled with dielectrics as shown in fig. The dielectric constants are K1 and K2 respectively. The capacitance will be

The combination is equivalent to two capacitors in series, each with plate area A and separation d / 2.C1=K1ε0A(d/2)=2K1ε0AdC2=K2ε0A(d/2)=2K2ε0AdThe equivalent capacitance C is given by1C=1C1+1C2∴ 1C=d2K1ε0A+d2K2ε0A=d2ε0A1K1+1K2=d2ε0AK1+K2K1K2or     C=2ε0AdK1K2K1+K2