Determination of the Charge of an Electron

Samuel G. Privett, New Mexico Institute of Mining and Technology


The purpose of this experiment was to determine the fundamental charge of an electron. This was accomplished by measuring the terminal velocities of drops of oil and measuring the voltages required to suspend the oil drops in an electric field while taking into account the effects of pressure on the viscosity of air. The voltage readings were calibrated by comparing the voltage displayed on the Millikan Oil Drop apparatus to the voltage reading of a Fluke multimeter, providing a 0.7% correction to the readings from the apparatus. Through this process, I found the charge of an electron to be 2.5 x 10-19 ± 1.5 x 10-19 C. The fundamental charge of an electron is reported to be 1.6 x 10-19 C (Haynes, 2014). My finding is within 58.2% of the reported charge of an electron. The result of this experiment could be improved further by taking data from more oil drops and taking better measurements of air pressure and temperature to provide for better corrections to the air viscosity.