1. The problem statement, all variables and given/known data in a millikan type apparatus, the horizontal plates are 2 cm apart. with the field switched off, an oil drop is observed to fall with a steady velocity of 2 x 10^-4 m/s. when the field is on, the upper plate being positive and the drop just remains stationary when the pd between two plates is 1150 v a/ calculate the radius of the oildrop b/ how many electrons charges does it carry 2. Relevant equations a/ w=fd m g = 6 phi η r v b/ fe = w q Δv/d = m g 3. The attempt at a solution a/ i don't understand how much is m, and η it is not mention in the question. what should i do? where should i put V? b/how much is m?