Millikan and the contact potential question on the photoelectric effect experiment

Abstract It will be presented in this paper the theoretical and experimental Millikan's approach to the contact potential question in his experiments about the photoelectric effect. The 1923 Nobel prize won by Millikan, had as motivation his experiments which resulted on the electron charge (oil drop experiment) and Planck constant (photoelectric effect experiment) measurements. The precision with which Millikan obtained the Planck constant is due to the importance Millikan attributed to the contact potential between two electrically connected metals. Presenting his calculations on the contact potential in one of his 1916 papers, Millikan showed one result subtly wrong, apparently not perceived by the scholars of the subject. In 1921, Millikan corrected the erroneous equation without mention the 1916 mistake. If this mistake was not due to bad digitation, apparently there is no plausible justification for their occurency.