In a particular Millikan oil-drop apparatus, the plates are 2.25 centimeter apart. The oil used has a density of 0.835 g/cm3, and the atomizer that sprays the oil drops produces drops of diameter 1.00 × 103 mm.
a. Find what strength of electric field is needed to hold such a drop stationary against gravity if the drop contains five excess electrons?
b. Find the potential difference across the plates to produce this electric field?
c. If another drop of the same oil requires a plate potential of 75.3 Volt to hold it stationary, find how many excess electrons did it contain?