  The problem of interest in this article are waves on a layer of finite depth
governed by the Euler equations in the presence of gravity, surface tension,
and vertical electric fields. Perturbation theory is used to identify canonical
scalings and to derive a Kadomtsev-Petviashvili equation withan additional
non-local term arising in interfacial electrohydrodynamics.When the Bond number
is equal to 1/3, dispersion disappears and shock waves could potentially form.
In the additional limit of vanishing electric fields, a new evolution equation
is obtained which contains third and fifth-order dispersion as well as a
non-local electric field term.
