Charged droplet experiments

Abstract

The velocity and charge of individual charged droplets of oil accelerated through 12 and 13 kv. have been measured. From these measurements, the oil density, and the accelerating potential, computations were made of the charge-to-mass ratio, the mass, and the radius of the droplets. The charge-to-mass ratios were 0.01 to 5 coulombs per kilogram and the droplet radii were 0.1 to 10 microns. The charged oil droplets were produced at the point of a hollow stainless steel needle maintained at a high (12–13 kv.) positive potential. Rayleigh's theory on the instability of charged liquid drops predicts a maximum limit of charge-to-mass ratio as a function of radius above which the drops become unstable. The maximum observed charge-to-mass ratios of the oil drops at any radius were found to lie very close to the theoretical curve predicted by Rayleigh's theory. This limit was about a factor 50 below the field emission limit predicted on the basis of E. W. Müller's work on field emission.