Solving a problem in physics section 59 paragraph 69 el

69. A plate made from hard rubber thickness d = 2 mm and S = area of 300 cm2 were placed in a uniform electric field intensity E0 = 1 kV / m, is positioned so that its field lines are perpendicular to the flat surface. Find: 1) the density of σ ´related charges on the surface of the wafer; 2) the energy W of the electric field concentrated in the plate.