ON MEASUREMENT OF SMALL PHOTO-CURRENTS ON A DROPPING MERCURY ELECTRODE

An instrument is described with which small photo-currents on a dropping mercury electrode can be measured automatically. A mercury arc lamp in conjunction with interference filters is used as a source of essentially monochromatic light. Chopping of the light beam and synchronous rectification of the resulting alternating current makes it possible to measure photo-currents, even if these are several orders of magnitude smaller than the simultaneously flowing double-layer charging current. Results obtained with the instrument are given, and are discussed in the light of recent theories of electron photo-emission. © 1969.