When I was taught Gauss's law. My teacher used a cylindrical Gaussian surface to find the electric field above an infinite uniformly charged plate. What I have trouble understanding is why the plate has to be infinite in order for the arguments to work? http://farside.ph.utexas.edu/teaching/302l/lectures/node27.html Here's a link explaining the way to use Gauss's law to find the electric field. But what if I repeat the same thing with a finite plate? I know it won't work but I want a good explanation of why it won't work?