1) A thin, horizontal 0.10m x 0.10m copper plate is charged with 1.0x10^10 electrons. If the electrons are uniformly distributed on the surface, what are the strength and direction of the electric field 0.1mm below the centre of the bottom surface of the plate? (Note: copper is a conductor, so all excess charges will be on the surface) Should I use the formula E=(eta)/(epsilon_o), or should I use E=(eta)/(2*epsilon_o) ? Why? [E=electric field, eta=surface charge density] Second question: to find the surface charge density eta=Q/Area Should I substitute 1.0x10^10 for the charge Q or should I substitute 5.0x10^9 (half of the electrons) as the charge Q? I am really having some problem understanding how to calculate this...can someone help me? Thank you!