A charged particle (either proton or electron) is moving rightward between 2 parallel charged plates separated by distance d = 2mm. The plate potentials are V1 = -70.0 V and V2 = -50.0 V. The particle is slowing from an initial speed of 90.0 km/s at the left plate. a) Is the particle an electron or a proton? b) What is its speed just as it reaches plate 2? i used the equation V2 - V1 = -W_E / q (W_E is the negative of the work done by electric field). so i have 20 = -E(.002) and i got E = -10000 N/C. i don't know what to do next. how do i tell if its a proton or electron?