Revisiting the Millikan Oil Drop Experiment

Anna Smith, New Mexico Institute of Mining and Technology


We present the finding s of a simulated oil drop experiment to determine the charge of an electron. An apparatus with an oil chamber, telescope and CCD camera were used to keep track of 12 individual drops of oil was c of various sizes . Before taking any measurements, the voltage alibrated by comparing 7 different voltage measurements from the apparatus with a voltmeter. Those measurements were plotted against each other to achieve calibration, which was included in the measurements taken from the oil drops. The distance between each division on the CCD program was also calculated by sticking a thin wire of known diameter into the opening of the oil drop chamber and scaling the division on the screen based on wire diameter. For each drop we measured the fall time and balancing voltage, which allowed the drop radius, velocity, and charge to be calculated. The charge of an electron was calculated using the ratios method subtracted, , where for each charge calculated the largest whole number was then the remaining decimal was divided by multiplied by the smallest measured charge . The the smallest trail charge, and finally average 5.4x1020 ± 3.9x1020 charge of an electron was found to be Coulombs. While this is not too far off from the published value of an electron, this experiment could have benefited from more oil drop measurements and trying different types of oils to compare the results.