Part A: What must the charge (sign and magnitude) of a particle of mass 1.40g be for it to remain stationary when placed in a downward-directed electric field of magnitude 700 N/C?
Part B: What is the magnitude of an electric field in which the electric force on a proton is equal in magnitude to its weight?
Use 1.67x10^-27 kg for the mass of a proton, 1.60x10^-19C for the magnitude of the charge on an electron, and 9.81m/s^2 for the magnitude of the acceleration due to gravity.