This work is based on a problem situation, in the context of the electromagnetic theory, presented to students in various undergraduate classes in physics at the Universidade Federal do Rio Grande do Norte (UFRN). The main lines of reasoning developed by student were concentrated in three solutions reuniting diverse presented opinions. The analysis of those solutions indicates the existence of mistakes, which became an important part in understanding the correct approach. This practice of valuation of the errors for the construction of the appropriate solutions revealed to have a high didactic scope.
transient; Maxwell's equations
