Question: how was the charge of an electron discovered
Answer: The electron 's charge was more carefully measured by the American physicists Robert Millikan and Harvey Fletcher in their oil - drop experiment of 1909 , the results of which were published in 1911 . This experiment used an electric field to prevent a charged droplet of oil from falling as a result of gravity . This device could measure the electric charge from as few as 1 -- 150 ions with an error margin of less than 0.3 % .