1. The problem statement, all variables and given/known data A slab of dielectric of thickness a and relative permittivity ε is placed in a uniform external field E whose field lines make angle θ with normals to the surface of the slab. What is the density of polarization charge on the surface of the slab? Neglect end effects. 2. Relevant equations P⋅dS = σp D = P + ε0E 3. The attempt at a solution The correct answer is ± ε0Ecosθ(1-1/ε). I assume there is no free charge in the dielectric so D is zero. But I can't get the answer. Does someone can help me?