Electrostatic Deformation of Liquid Surfaces by a Charged Rod and a Van de Graaff Generator

Authors of physics textbooks frequently use the deflection of a thin, vertically falling water jet by a charged balloon, 1–3 comb, 4–6 or rod 7–9 as a visually appealing and conceptually relevant example of electrostatic attraction. Nevertheless, no attempts are made to explore whether these charged bodies could cause visible deformation of a horizontal water surface. That being so, we were quite surprised when we discovered that a 19th-century French book 10 contained a drawing showing an appreciable deformation of an oil surface caused by a charged rod. When we initially tried to recreate this electrostatics demonstration, we didn't succeed in reproducing the effect with a charged rod. Despite the initial unsuccessful try, we were not discouraged and we modified the demonstration a little bit, finding that it was possible to cause visible deformations of different liquid surfaces by using a Van de Graaff generator, as we will explain later.The work on this article was started during the visit of the first author to the Universitat d'Alacant (Spain), planned within the research project Active Physics Learning Online, supported by the CONACyT (Mexico). Financial support from the Centro de Estudios Iberoamericanos Mario Benedetti