Electrical charging of water drops in polarizing electric fields

Measurements were made of the electric charge acquired by drops of mean radius of about 750 μm as they fell through a cloud of water droplets of mean radius 16 μm, in the presence of a vertical electric field E, the value of which could be varied from 4.5 to 27 kV m^-1. It was found that the proportion of interactions which resulted in separation (and, therefore, in electric charge transfer, as a consequence of the inductive process of electrification) decreased from about 1% in the weaker fields to about 0.2% in the strongest ones. This work suggests that the collisions between polarised raindrops and cloud droplets in natural clouds could give rise, very effectively, to the production of electric fields of about 30 kV m^-1 but that significantly larger fields could not be produced since all collisions in higher fields would result in permanent coalescence.