A parallel- plate capacitor of area A, plate separation d and capacitance C is filled with four dielectric materials having dielectric constant k1,k2,k3 and k4 as shown in the figure below. If a single dielectric material is to be used to have the same capacitance C in this capacitor, then its dielectric constant k is given by
2k=3k1+k2+k3+1k4
k1,k2,k3 are in parallel so Arithmetic mean.
keq=k1+k2+k33
keq is in series with k4.So harmonic mean.
⇒2k=1keq+1k4⇒2k=3k1+k2+k3+1k4