This paper presents an analysis of the answers of 74 college students to questions regarding Gauss's law for electricity in an introductory physics course. From these answers three categories of difficulties were identified: 1) those dealing with the physical meaning of the law, 2) those referring to its mathematical operacionalization, and 3) those regarding the concepts of Gaussian surface and electric field flux. These difficulties were examined in the light of Johnson-Laird's mental models. The main reason of such difficulties would be the fact that students were not able to construct mental models and, even less, assimilation schemes, that would provide some meanings to the law and to the involved concepts. Possibly, the instruction (classes and textbook) they got was not appropriate to help them in the construction of these models and schemes.
physics learning; Gauss's law; mental models
