BACKGROUND: Commonly in electric circuit theory courses, circuit laws are first introduced in the context of direct current (DC) electricity and first thereafter are alternating currents (AC) introduced. The extension of DC-theory to AC is quite easily done mathematically but is conceptually difficult for students. Engineering students have difficulties in understanding phase relationships and phasor representations in AC-electricity. Indeed, it has been suggested that phase should be seen as a threshold concept.

PURPOSE: The purpose of this study was to investigate if a re-designed introductory electric circuit course could improve students’ understanding of important concepts in AC-electricity.

METHOD and COURSE DESIGN: The course was re-designed introducing AC and DC electricity simultaneously. DC was introduced as a special case of AC with requency equals zero. The re-designed course was taught for the first time during the spring semester 2014 and a new textbook was written. A conceptual test was developed and first administered in 2013 to serve as a baseline and in subsequent years to evaluate the revised course. In 2014 the students’ courses of action in selected lab-groups were video-recorded.

RESULTS: In the first revision cycle many students had difficulties to complete the labs in time. Students revealed a mixed response towards the revised course and the results on the conceptual test showed neglible improvement. In the second cycle revisions the number tasks were reduced and focus was laid on tasks that were identified as most important for contributing to the development of student understanding. As a result the learning gain improved with an effect size (Cohen’s delta) of 0.56. Also the course and the textbook were very well appreciated. In the third cycle only small revisions are made.

CONCLUSION: The results show that that AC-electricity can be taught concurrently with DC. However, two revisions cycles was needed which demonstrates that curriculum development needs a sustained effort over a considerable period of time with continuous revisions in light of gained experiences. In further revision we will continue to refine the labs and to develop appropriate interactive lecture demonstrations for the lectures and to develop the problems.