Figure 2-16 A sphere of radius R with uniformly distributed surface charge {70' (a) Symmetrically located charge elements show that the electric field is purely radial. (b) Gauss's law, applied to concentric spherical surfaces inside (f < R) and outside (f > R) the charged sphere, easily shows that the electric field within the sphere is zero and outside is the same as if all the charge Q = 4 TrR'luo were concentrated as a point charge at the origin.