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Why Does a Stream of Water Deflect in an Electric Field?

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G. K. Vemulapalli and S. G. Kukolich

Department of Chemistry, University of Arizona, Tucson, AZ 85745

J. Chem. Educ., 1996, 73 (9), p 887

DOI: 10.1021/ed073p887

Publication Date (Web): September 1, 1996

Abstract

A popular lecture demonstration shows a stream of water bending in the presence of an electrified object. We have quantitatively analyzed this phenomenon after experimenting with controlled electric fields. The following are our conclusions. (i) The electric field must be nonuniform for this effect to be observed. The electric force is proportional to the product of the field and its gradient. In case of water, these are of the order of 10⁵ V m^-1 and 10⁸ V m^-2. (ii) The effect is readily observed with water because the gravitational force opposing the deflection is small due to lighter mass of water molecules. (iii) Since electric fields induce dipole moments, even nonpolar molecules show deflection if the field is strong enough. Statements in many textbooks about this phenomenon are misleading since they do not point out the importance of nonunimformity of the field, the relative magnitudes of gravitational and electric forces, and the possibility that induced dipoles also undergo deflection.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Demonstrations

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Water / Water Chemistry

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Electrical Deflection of Polar Liquid Streams: A Misunderstood Demonstration
Maryam Ziaei-Moayyed and Edward Goodman , Peter Williams
Journal of Chemical Education2000 77 (11), 1520
- Electrical Deflection of Polar Liquid Streams: A Misunderstood Demonstration
  Maryam Ziaei-Moayyed and Edward Goodman , Peter Williams
  Journal of Chemical Education2000 77 (11), 1520
  The electrical deflection of polar liquid streams, commonly used as a textbook illustration of the behavior of polar molecules, is shown to be due to the formation of electrically charged droplets in the polar liquid stream, induced by a nearby charged ...
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