1) An oil drop of mass 4.92 x 10-15 kg is balanced between two large, horizontal parallel plates 4.3 cm wide, 7.2 cm long and 1.2 cm apart, maintained at a potential difference of 510.4 V. a) Draw a neat fully labelled diagram of the problem including forces, charges and distances.

b) How many elementary charges does the electron have?

c) Explain clearly to a Grade 9 student how Millikan was able to use an apparatus like this to determine that charge is always an integral multiple of an elementary charge.