Two square plates (l×l) and dielectric l2×t2×l are arranged as shown in figure. Find the equivalent capacitance of the structure.

We can make equivalent circuit of given system in two ways as in Figs. (a) and (b). But (b) is wrong and (a) is correct.Here C1=ε0A/2t/2=ε0At         C2=Kε0A/2t/2=Kε0At and C3=ε0A/2t=ε0A2tNow,  Ceq=C1C2C1+C2+C3                =ε0At3K+12(K+1)