Charge transfer between uncharged water drops in free fall in an electric field

Abstract

The charging of uncharged, equal or very nearly equal radius drops falling freely in an electric field has been observed to occur in two different modes. When the electric field exceeds a threshold value that is a function of drop size, the charge is transferred via a spark in the air between the near surfaces of approaching drops. Below this threshold, the rate of charge transfer is slower and varies with the conductivity of the water. The onset of the spark transfer mode occurs when the voltage and the separation distance between the surfaces of the drops reaches the minimum sparking potential required for breakdown between parallel plate electrodes. The ambient field strength at the onset of sparking varies with drop size according to the theoretical enhancement of the local field between the surfaces for a fixed separation. The information obtained in this way assists studies of the electrification of clouds and cloud particles and the growth of precipitation in thunderstorms. The previous work on radio emission from colliding charged drops can presumably be extended to include uncharged and weakly charged drops in electric fields.