1. The problem statement, all variables and given/known data A parallel plate capacitor has two conducting plates seperated by a vacuum. The distance is D and the area of each plate is A. An alpha particle with mass M and charge Q is placed on the positively-charged plate, between the plates. It shoots through a small hole in the negatively charged place with speed S. What is the magnitude of the uniform electric field between the plates? How much charge lies on the positively-charged plate? How much energy is stored in the capacitor's electric field? 2. Relevant equations C=Q/V V=Ed C=(A/d)(epsilon_o) 3. The attempt at a solution For the first question, I can find the capacitence, C=(epsilon_0)(A/D), but I'm not sure where to go from here. For the second question, I could find Q using C=Q/V and use V=Ed but I need E from the first question that I don't know how to find! I'm not sure where the alpha-particle comes in to play!? Thank you!