Here's the problem: An infinately long cylinder of radius R has a volume charge density that varies with the radius as p = p0(a-r/b) where p0, a and b are all positive constants amd r is the distance from the axis of the cylinder. Use Gauss' law to determine the magnitude of the electric field at r<R and r>R. here's my logic for r < R: E = k * int[p*dV/r] = k*p0*int[(a-r/b)*dV/r] -Then sub in V=Pi*r^2*L (solved for r and integrate wrt V) but what is this L if it's infinate. Also what is the difference being inside or outside of the cylinder? is it just the limits of integration (ie 0-R, or R-r)? Thanks.