A parallel plate capacitor is made of two dielectric blocks in series.
One of the blocks has thickness $d_1$ and dielectric constant $k_1$ and
the other has thickness $d_2$ and dielectric constant $k_2$ as shown in
Fig. This arrangement can be thought as a dielectric slab of
thickness $d (= d_1+d_2)$ and effective dielectric constant k. The k is
