THE MILLIKAN OIL-DROP EXPERIMENT - MAKING IT WORTHWHILE

Improvements to the Millikan oil drop experiment as it is performed in teaching laboratories are described. Enhancement of the optics in the oil-drop apparatus greatly improves the visibility of the drops. Accu rate timing of their motion becomes possible since they are now bright and sharply focused. With improved timing, the parameters such as mic roscope calibration and plate separation can become the principal sour ces of experimental error. Methods are described to accurately determi ne these experimental parameters. The workload for the experimenter is greatly reduced by using a computer to: act as a smart stopwatch, cal culate the drop charge in real time, perform the statistics, and make records of the experiment. The convenience and speed offered by the co mputer, coupled with improved optics, relieves the eyestrain, fatigue, and frustration usually associated with this experiment. Nye's watch oil was used in this study. A return to Millikan's original iteration method for the correction to Stokes' law lowers the calculated charge for small drops by about 2%. With these improvements the calculated ch arges are sufficiently accurate that guesswork as to the multiplicity of their charge is essentially eliminated. A student typically obtains the value of the electronic charge accurate to about 1% with 1 h of e xperimentation. Student and instructor satisfaction are much improved. (C) 1995 American Association of Physics Teachers.