A proton with a kinetic energy of 1.2 × 10  ^-16 J enters a uniform electric field between two parallel plates. If the proton is to turn left, what should be the charge on the plates?

• A. both plates positive
• B. top plate negative and bottom plate uncharged
• C. top plate positive, bottom plate negative
• D. top plate negative, bottom plate positive

Answer: (C)