My physics book explains that this is because of the conservation of charge and the fact that charge doesn't accumulate at a certain point. Can someone please explain this in detail, especially the part where it says that charge can't accumulate. Another question which i think is similar is the amount of mass flowing into and out of a pipe. My professor used the conservation of mass to show that the mass of fluid flowing into the pipe is equal to the mass flowing out. Isn't it possible that the fluid accumulates inside the pipe and gets compressed, so that the mass flowing out will be less than the mass flowing in? Thanks!