Millikan’s Oil Drop Experiment

This is the Millikan’s Oil Drop Experiment, one of the most important experiments ever performed. Thomson had identified the electron as a charged particle in 1897 and had measured its charge to mass ratio.  Now Millikan took the next step allowing the charge on an electron to be measured.  He used oil drops each of which had a specific number of charges on them and placed them between two plates connected to a high tension voltage supply.  Altering the voltage on the plates causes the charged oil drops to move at various speeds depending on their charge.  Measuring these speeds indicates their masses.  This version of the experiment replaces the oil drops with tiny polymer balls.