1. The problem statement, all variables and given/known data A pair of infinite, parallel planes are equipotential surfaces. The plane at z = 0 has an electric potential of 0 and the plane at z = b also has a potential of zero. The electric field at b is 0 at time t at which there is a constant, positive charge density between the planes of Rho_naught. (i) Use Poisson's eqn. to write down the appropriate diifferential equation for 0 <= z <= b. (ii) Solve the equation to get the potential in terms of arbitrary constants. (iii) Use the resulting potential to find the vector electric field in terms of arbitrary constants. (iv) Use the boundary conditions to find the constants. 2. Relevant equations Poisson's eqn = Laplacian (Psi) = Del ^2 Psi = d2Psi/dx2 + d2Psi/dy2 + d2Psi/dz2 = -Rho_naught/epsilon_naught E = - Del(Psi) 3. The attempt at a solution Honestly I am at a loss. I don't understand how the E field can be zero everywhere at b if there is a charge density right next to it. I have no idea how time comes into this. Thanks.