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J4-11. Polar And Nonpolar Liquids


To demonstrate that non-uniform electric fields produce a force on polar molecules.


Electrophorus with insulated aluminum plate, water and carbon tetrachloride molecular models, squirt bottles of◙water and carbontetrachloride, point source for shadow projection.◙


There is a less toxic fluid which can be used in place of carbon tetrachloride, but we don't know what it is. If◙anyone knows, we would appreciate being told.

Setup Time

5 minutes.




An electrophorus is used to charge an aluminum plate. A stream of carbon tetrachloride (CCl4), a non-polar molecule, is sprayed in front of the charged plate; the stream of carbon tetrachloride is unaffected by the electric field of the plate. A stream of water (H2O) sprayed in front of the charged aluminum plate deflects strongly, indicating that the charge centroids of the positive and the negative charges are not the same. The non-uniform electric field rotates the molecules and exerts a force on the dipole electric dipole of a non-polar molecule. ◙◙Models of carbon tetrachloride and water


M. H. Davis, Electrostatic Field and Force on a Dielectric Sphere near a Conducting Plane - A Note on the Application of◙Electrostatic Theory to Water Droplets, AJP 37, 26-29 (1969).