An oil drop of mass 4.95 x 10-15 kg is balanced between two large, horizontal parallel plates 2cm apart, maintained at a potential difference of 420 V. The upper plate is positive. Calculate a) the charge on the drop, both in (i) coulombs and (ii) as a multiple of the elementary charge, b) and state whether there is an excess or deficit of electrons. Ensure that you have a clearly labelled diagram