written by Jake S. Bobowski and Jaklyn De Vos

An experiment that investigates the transition from conductive to dielectric screening of electric fields by a tube of water has been designed for senior physics undergraduates. A parallel-plate capacitor is used to generate a uniform electric field. Two concentric acrylic plexiglass tubes pass perpendicularly through the electric field generated between the plates. The region between the tubes can be filled with air or water. An electrode, suspended within the inner plexiglass tube, is used to sense the electric potential at its location. The sensor is designed so that it can be rotated to measure the potential at a second symmetric position. From the difference in the two potentials, the frequency dependence of the magnitude and phase of the electric field can be determined. With deionized water between the tubes, the magnitude and phase of the interior electric field was measured from 100 Hz to 300 kHz. The high-pass filter frequency response expected for a dielectric tube with non-negligible conductivity was observed. Fits to the data yielded a very reasonable experimental value for the ratio of the water's conductivity to its dielectric constant.

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Published November 17, 2015
Last Modified November 17, 2015

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