Parallel plate Capacitor with Composite dielectric

A parallel plate capacitor can also have composite dielectrics. Fig 1 shows such a capacitor.

Let b be the distance of separation between the two plates in meter. If the thickness of one dielectric is t meter , the thickness of the other dielectric is (d-t) meter. Let dielectric no.1 have permittivity ε₁ and the dielectric no.2 have permittivity ε₂. If each is considered as a separate capacitor, C₁=ε₁ ε₀ A/t & C₂=ε₂ ε₀ A/(d-t)

With a composite dielectric, the parallel plate capacitor can be considered as two capacitors in series. The total capacitance C therefore is given by—