Electrical Engineering ⇒ Topic : Parallel-Plate Capacitor with Composite Medium
Parallel-Plate Capacitor with Composite Medium
Suppose the space between the plates is occupied by three dielectrics of thicknesses d1, d2 and d3 metres and relative permittivities εr1, εr2 and εr3 respectively as shown in Fig.(a). The electric flux density D in the dielectrics remains the *same and is equal to Q/A. However, the electric intensities in the three dielectrics will be different and are given by
If V is the total p.d. across the capacitor and V1, V2 and V3 the p.d.s. across the three dielectrics respectively, then,
But Q/V is the capacitance C of the capacitor.
Different cases. We shall discuss the following two cases
(1) Medium partly air. Fig. (a) shows a parallel plate capacitor having plates d metres apart.Suppose the medium between the plates consists partly of air and partly of dielectric of thickness t metres and relative permittivity εr2. Then thickness of air is d - t. Using the relation (i) above, we have
(2) When dielectric slab introduced. Fig. (b) shows a parallel-plate air capacitor having plates d metres apart. Suppose a dielectric slab of thickness t metres and relative permittivity εr2 is introduced between the plates of the capacitor.
Using the relation (i) above, we have,
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