I understand how to use Gauss's law to calculate the electric field at some point for say a sphere with charge distributed uniformly in it. I am bit confused, though, about calculating the electric field at some point for a non-uniform charge distribution. For example, say that I have a spherically symmetric negative charge distribution around the origin of my reference frame, with charge density p(r) given by -0.5e^(-r), where r is the distance from the origin (IE, the radius of a given sphere) (so, p(0) = -0.5 and p(1) ~ -0.2). If I wanted to calculate the magnitude of the electric field vector at some radius r, how would I do this? Let's say I wrap up a portion of the charge distribution in a Gaussian sphere of radius r. The net flux through all tiles on this spherical Gaussian surface would be 4*pi*(r^2)*E, where E is the magnitude of the electric field at all points on the surface. Then, using Gauss's law and solving for E, I get E = [k / (r^2)]Qenc(r) Where Qenc(r) is the total charge enclosed by the closed surface at radius r. This is where I get stuck. Knowing the charge density function p(r) (in units C / m^3, let's say), how do I find the net enclosed charge by the sphere of radius r? Any help would be appreciated.