Flux and nonconducting shells. A charged particle is suspended at the center of two concentric spherical shells that are very thin and made of nonconducting material. Figure (a) shows a cross section. Figure (b) gives the net flux ? through a Gaussian sphere centered on the particle, as a function of the radius r of the sphere. (The vertical axis is marked in increments of 5.0 105 N·m2/C with ?s = 2.5 106N·m2/C )