1) Show that the component of the electric force normal to any flat surface with a uniform charge density σ is given by F⊥=σΦE where ΦE is the electric flux through that surface due to an external electric field.
2) An insulating hemisphere with radius R and charge Q distributed uniformly over its flat, circular surface lies above a large plane with uniform charge density σ. The axis of the hemisphere is oriented vertically. For what mass M could the hemisphere remain stationary?
3) If the hemisphere and the plane share the same charge density of 100 μC/m2 and the hemisphere has a radius of 3.00 cm, what would be its upward acceleration if its mass were 100 g?