I have two questions: 1) Is it in general assumed that the parallel plates of a capacitor are fixed to some surface or is there a force that counteracts the attractive force between the plates whenever one considers a typical problem involving capacitors? 2) Consider a dielectric of length L and two capacitor plates of length L. Suppose the dielectric is wedged halfway in between the two plates. Why does the capacitor attract the dielectric into itself? The only force I can think of is the force due to the electric field between the plates, but this force is perpendicular to the direction of displacement into the capacitor, hence cannot be responsible for such a displacement. Is it the fringe field at the ends of the capacitor or is there some other force I missed?