Hi everybody, I am getting confused by a very simple problem: lets take an infinite sheet electrically charged with a surface density σ. Because the sheet is infinite, we can first determine that the electrical field on both side contains only components normal to the sheet. If the plate is surrounded on both side by vacuum, we know from the symmetry principle that the components of the electrical field on both sides of the sheet have the same magnitude and opposite directions. From Gauss law, we can then determine that the magnitude is σ/2ε0. Now, lets consider the case where the sheet is surrounded on one side by dielectric material 1 with relative permittivity ε1 and on the other by material 2 with relative permittivity ε2. I want to determine the characteristics of the electrical field E1 and E2 on both sides of the sheet. My first reasoning approach was that, compared to the vacuum case, the electrical field is simply reduced by a factor ε1 in material 1 and by a factor ε2 in material 2 due to the induced polarization, so that we would get E1=σ/2ε0ε1 and E2=σ/2ε0ε2. Well, it cannot be true as it violates the continuity condition on the electric displacement (D2=D1+σ → ε2 E2=ε1E1+σ → σ=0), but it confuses me. My second approach is to consider first the continuity condition of the electric displacement which tells that ε2E2=ε1E1+σ. But then I need a second equation to determine E1 and E2. Using some numerical software, I observed that E1=E2 which leads to E1=E2=σ/(ε0ε1+ε0ε2). However, the fact that E1=E2 is really counter-intuitive to me as the problem appears to be non symmetric. Could someone give me some arguments on why the first approach is not correct? Is the second approach correct? If yes, how to justify the assumption E1=E2?