The space between the plates of a parallel-plate capacitor
is filled consecutively with two dielectric layers 1 and 2 having
the thicknesses d1 a nd d2 and the permittivities 81 a nd 82 respectively.
The area of each plate is equal to S. Find:
(a) the capacitance of the capacitor;
(b) the density a' of the bound charges on the boundary plane if
the voltage across the capacitor equals V and the electric field is
directed from layer 1 to layer 2.