The system is a parallel plate capacitor, top plate has charge density sigma, bottom play has charge density -sigma. I'm looking for the "field momentum" inside the cubic volume Omega shown in the picture. My book (Griffiths) is a little unclear on exactly what this is, and seems to be saying that the momentum is proportional to the Poynting vector ExB, so since there doesn't seem to be a magnetic field, this would suggest the field momentum is zero. Is this correct? The only problem I'm having is that, later in the problem, it asks if there's a net flow of field momentum into the cube, so I'm thinking there's more to the problem than what I'm seeing. Could anyone help clear this up? Thanks.