Millikan Oil Drop Experiment:
In 1909, American physicist R. Millikan measured the charge of an electron using negatively charged oil droplets. The measured charge (e) of an electron is −1.60×10−19 Coulombs.
Using the measured charge of electron, we can calculate the mass of electron from e/m ratio given by J. J. Thomson’s cathode ray experiment.
m=e−1.76×108Putting e=−1.60×10−19 Coulomb,m=9.1×10−28 gram.