1. The problem statement, all variables and given/known data The electric field intensity in polystyrene (relative permittivity 2.55) filling the space between the plates of a parallel plate capacitor is 10kV/m. The distance between the plates is 1.5mm. Calculate the surface charge density of free charge on the plates, and the surface density of polarization charge 2. Relevant equations rho s = D dot an 3. The attempt at a solution --- I am having a hard time seeing how the surface charge density equals the d field normal to the surface in this case?