Anton Potočnik

                            at ETH Zürich

Bending mercury stream with electrostatic force

One of our recent projects involved a detailed understanding of the mechanism behind bending of liquid streams in electrostatic potential. To test our understanding we performed two experiments, one with tap water, where conductivity is low, and the other with strongly conducting liquid – the mercury.

Unfortunately, the explanation why the stream of water is bent in electrostatic potential is often wrong. People try to explain the observed electrostatic force in terms of dielectrophoresis where a material with a large dielectric constant has lower energy in the region of higher electric field than where electric field is lower. Although this force exists it is negligible compared to the electrostatic force between charged plastic rod and the opposite charge that accumulates in the water stream. The same phenomenon is used for example in Kelvin water dropper experiment.

More information can be found in
M. Ziaei-Moayyed and E. Goodman. J. Chem. Educ. 77 (11), 1520 (2000).

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