Hello everyone i'm confused on where I should go next with this problem. It is found experimentally that the electric field in a ceritan region of Earth's atmosphere is directed vertically down. At an altitude of 300m the field has a magnitude 60.0 N/c; at an altitude of 200m, the magnitude is 100 N/c. Find the net amount of charge contained in a cube 100m on edge, with horizontal faces at altitudes of 200 and 300m. I posted a picture of what I think it should look like: http://img331.imageshack.us/img331/143/physicssss8uv.jpg [Broken] I found the electric flux at 200 and 300m (values are on image): The flux at 300m should be negative. So then I used Eo(Flux) = q_enclosed for both faces and found. At 300m the enclosed charge is 3.186x10^-5, and at 200m I found the enclosed charge to be 5.31x10^-5. But now i'm lost on what i should do. THe answer is 3.54x10^-6 C. Thanks.