Vernier Software and Technology
Vernier Software & Technology

Electric Field Due to a Line of Charge


Consider a thin insulated rod that carries a known negative charge Qrod that is uniformly distributed. It is possible to determine the electric field along a line perpendicular to the rod that passes through its center using the following equation – often derived in introductory texts:

\vec E_{{\text{rod}}}^{{\text{theory}}} = \frac{{\left( {k{Q_{{\text{rod}}}}} \right)}}  {{r\sqrt {{r^2} + {{(L/2)}^2}} }}\hat i

where L is the length of the charged part of the rod, r is the distance from the test charge to the center of the charged part of the rod, and Qrod is its total charge. The constant k is the well-known Coulomb constant.


In this activity, you will

  • Examine a digital movie of a charged rod exerting a force on a hanging “test charge” along with a Logger Pro analysis to determine if the theoretical equation describes the relationship between r, L and the measured electric field, \vec E_{{\text{rod}}}^{{\text{meas}}} at the location of the test charge.

Software for Experiment

This experiment uses Logger Pro software for video analysis. The video for analysis is included with the lab book.

Experiment 27 from Physics with Video Analysis Lab Book

<em>Physics with Video Analysis</em> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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