Two square plates (l×l) and dielectric l2×t2×l 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=ε0AtC2=Kε0A/2t/2=Kε0At  and  C3=ε0A/2t=ε0A2tNow, Ceq=C1C2C1+C2+C3=ε0At3K+12(K+1)