Variation of Photoelectric Current with Temperature. The photoelectric current from pure potassium, in highly exhausted cells, is found, contrary to previous belief, to vary with the temperature, and in the sense of the temperature change. The temperature range investigated was from room temperature to the temperature of liquid air; the variation of the photoelectric current with temperature is negligible above 0°C but becomes greater the lower the temperature. The change in photoelectric current is greater the lower the frequency of the exciting radiation, and occurs in both the normal and selective photoelectric effects.
Variation of Surface Work Function with Temperature. The variation of photoelectric current with temperature is shown to be in harmony with the supposition that the work function of the surface is altered. Such an alteration of the work function is shown experimentally by the occurrence of a bodily shift along the voltage axis of the voltage-current curve of a photo-sensitive cathode when the potassium, which is changed in temperature, is the anode. It is further checked by the change in the long wave-limit of photoelectric emission of the surface whose temperature is varied. On cooling potassium from +20° to −180°C its work function is increased by about 1/5 volt.
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