Imagine an oil drop weighing three to ten kg suspended between two plates that are separated by 1.3cm. The potential difference between the plates is 340 volts. Consider the following question: “How many excess electrons does this fall have?”
A single atom’s charge is 1.60×10-19 Coulombs. The charge of an oil drop is 2.4×1018 Coulombs. If the drop contains three electrons, it will have three excess electrons. Divide this number by the change of charge of the two other electrons. Therefore, the drop has three excess electrons. In addition to its weight, the charge of an electron is 1.60×10-19 coulombs.