  Helping students learn why Gauss' law can or cannot be easily applied to
determine the strength of the electric field at various points for a particular
charge distribution, and then helping them learn to determine the shape of the
Gaussian surfaces if sufficient symmetry exists can develop their reasoning and
problem solving skills. We investigate the difficulties that students in
calculus-based introductory physics courses have with the concepts of symmetry,
electric field and electric flux that are pivotal to Gauss' law of electricity.
Determination of the electric field using Gauss' law requires discerning the
symmetry of a particular charge distribution and being able to predict the
direction of the electric field everywhere if a high symmetry exists. It
requires a good grasp of how to add the electric field vectors using the
principle of superposition, and the concepts of area vector and electric flux.
We administered free response and multiple-choice questions and conducted
interviews with individual students using a think-aloud protocol to elucidate
the difficulties students have with the concepts of symmetry, electric field
and electric flux. Here, we discuss student responses to some questions on a
multiple-choice test administered to them. The test can be used as a teaching
and assessment tool.

Physics Education