Assessing physics teachers' pedagogical content knowledge of heat and temperature through a vignette based instrument

This study aims to develop a vignette based instrument to probe in-service physics teachers' PCK of heat and temperature. The instrument focuses on two dimensions of PCK, namely (1) knowledge of student understanding and (2) knowledge of instructional strategies. The procedure of the instrument development consisted of conceptualizing PCK, developing preliminary items, conducting the first round of cognitive interviews, developing a comprehensive item pool, conducting the second round of cognitive interviews, administering the final instrument, and conducting descriptive statistics. The final form of the instrument consists of 24 items, with 12 items in the Knowledge of Student Understanding section and 12 items in the Knowledge of Instructional Strategies section. A total of 99 in-service physics teachers and 10 non-physics teachers participated in the study. To ensure the validity of the instrument, expert opinions were taken, cognitive interviews were conducted, and scores of physics and non-physics teachers were compared. Item analysis, item-total correlation, Cronbach's alpha correlation, and inter-rater correlation were conducted to evaluate the reliability of the instrument. The results of the study suggest that in-service physics teachers mostly made too general interpretations regarding student alternative conceptions. The physics teachers' interpretations of alternative conceptions of temperature were more sophisticated compared to heat and heat conduction. Similarly, most of the teachers' answers to items probing their knowledge of instructional strategies were false/irrelevant. Their performance on items eliciting knowledge of analogies and demonstrations was insufficient.