By measuring the difference in how fast they fell, he was able to calculate the charge on an oil drop. (He did this by equating Coulomb's law to Newton equations of motion). After repeating this experiment several times, he deduced that all his answers were whole number multiples of 1.6 * 10-19 Coulombs (that's a decimal place followed by 18 zeros and then 16). He thus deduced that the charge on one electron was 1.6*10-19 C. He was also able to deduce the mass of an electron using the charge to mass ratio.
Answered by: K Shaban, CS/Physics Student, Carnegie Mellon
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