The problem statement, all variables and given/known data Suppose I am undertaking an experiment using a scanning electron microscope in which there is a positively charged plate underneath the target sample. I want to find the change in energy of the electron due to a positive voltage on this plate from the point it leaves the electron gun to the point it hits the sample. The only things I know are the voltage on the plate, the distance from the gun to the sample and the dimensions of the plate/sheet. The attempt at a solution My main question is can this be solved or do I need more information? At the moment I can only think of a way to do it by measuring the potential gradient above the plate to get the electric field. I know the electric field due to a finite sheet and I know that E = -∇V. Since the electron is directly above the sheet only the gradient in the z-direction(beam direction) has an influence, then once I get the electric field I can solve for the force and find the change in velocity. I apologise if this is a simple problem, it's been a while since I did electromagnetism. Thanks in advance.