Quantitative analysis of the electric dipole on finite sized graphite sheets

Abstract

Portable pop-up spectroscope Phys. Teach. 50, 443 (2012) Video-based spatial portraits of a nonlinear vibrating string Am. J. Phys. 80, 862 (2012) Analyzing simple pendulum phenomena with a smartphone acceleration sensor Graphite sheets are commonly used in introductory physics laboratories to model electric potential patterns for systems such as dipoles and parallel plates. Usually, silvered ink pens are used to draw patterns on the sheets and appropriate voltages are then applied. Quantitative experiments are often done at the intermediate level. Students are often puzzled by the failure of the patterns to confirm to the theoretical figure in the manual that came with the kit. I discuss measuring difficulties and some of the common theoretical methods for analyzing edge effects on the sheets.

High-density electric potential plots

“…We have chosen to show as an illustrative example the electric potential for the dipole, an iconic diagram that appears in practically every Freshman physics textbook. This example, on the other hand, has received relatively little attention in the physics education literature [1][2][3]. Our main result qualitatively confirms the diagram to within the practical limitations of our experiment.…”

“…We will be happy to make the following available upon request: set-up assembly instructions, raw and filtered data for figure 4, and an instructional video for Freshman physics lab showing students how to use the apparatus shown in figures 1 and 2 to produce contour plots. Finally, we intend to verify agreement with the more advanced expressions given in [1] in future work.…”

“…The conductive sheet is finite. As shown in [1], this causes significant and unavoidable deviations from the arrangement of two dipoles in an infinite plane, especially near the edges of the paper. Finding a larger piece of conductive paper may help reduce this problem.…”

“…Data points near the electrodes are scarce due to the obstruction of the pins, and the peaks appear a little skewed, probably because the probe has to go around the pins. The conductive sheet is too small to allow the potential to become flat far from the electrodes and the paper's boundary conditions contribute to further distortions of the potential [1]. Still, the essential shape is there.…”

“…Typical Freshman experiments for mapping electric potentials use a sheet of conductive paper with electrodes, and instruct the students to take up to a few hundred measurements with the probes of a voltmeter. From such data two-dimensional equipotential plots are produced via interpolation [1]. In this paper we modify the standard equipment to produce highly detailed plots of the potential.…”