1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution 1) the first question is easy,it is (C) because these charged balls are repelled from the similarly charged plates and accelerate towards the negatively charged plate,and once thy stick to the second plate they transfer double the charge they initially had (to the plate) and become oppositely charged. the same thing happens again and again in a periodic way(which is in no way simple harmonic). this discrete charge transfer at particular instants of time causes a current to flow(discrete current). 2) the second one i got wrong,i do not know why. i assumed that the average current is proportional to the velocity of the balls,i can relate the velocities to the potential applied as follows (velocity)^2 proportional to (potential diff) this is directly from the work energy theorem now (velocity) proportional to (potential diff)^1/2 from this and the previous assumption we see that (avg current) proportional to (potential diff)^1/2 and so the correct answer is (C) but in their answer keys it is given the answer is (D) (ie proportional to V^2) i don't see how this can be.