http://img404.imageshack.us/img404/4148/gauss3j.png (infinitly long) [itex]\Phi=\Phi_{0}(1-{r \over R}) {C \over m^2}[/itex] What's the charge of the cylinder of length L? Again, almost everything was wrong...
You need to be much clearer in the problem statement and your work. Is the cylinder hollow? What do r, R, [tex]\Phi[/tex], and [tex]\Phi_0[/tex] represent? Also, it's probably OK to write notes in your homework like "the electric field points radially outward so the flux through the top and bottom of the gaussian cylinder is zero" rather than relying on vague drawings
ok, now I got the following: Q=integral of /rho(1-r/R) times rdr d/phi dl Which is the answer for the question of what's the charge of the cylinder L. How to calculate it?