The gap between the plates of a prallel-plate capacitor is filled up with two dielectric layers 1 and 2 thickness `d_(1)` and `d_(2)` permittivities `epsilon_(1)` and `epsilon_(2)` and resistivities `rho_(1)` and `rho_(2)`. A dc voltage `V` is applied to the capacitor with electric field directed from layer 1 to layer 2 find `sigma` the surface density of extraneous charges at the boundary between the dielectric layers and the condition under with `sigma = 0`.
