A Van de Graaff generator is a device that accumulates electrons on a large metal sphere until the large amount of charge causes sparks. As you'll learn in Chapter 23, the electric field of a charged sphere is exactly the same as if the charge were a point charge at the center of the sphere. Suppose that a 25-cm-diameter sphere has accumulated 1.0 × 1013 extra electrons and that a small ball 50 cm from the edge of the sphere feels the force F⃗ =(5.0×10−4 N, away from sphere).