Lecture demonstrations in modern physics: Quality vs. quantity

In a study conducted in modem physics courses, our investigation shows that inappropriate and an excessive number of demonstrations can lead to ineffective results. We carefully observed and recorded the activities done in all lectures in two modem physics classes throughout a quarter and analyzed students' responses to the end of the quarter questionnaires. We found a significant number of students did not recall many of the in-class demonstrations and were confused about the results of different demonstrations they had seen in lectures. In this paper, we will explore the possible reasons for this outcome and discuss implications for instructors who use demonstrations in lectures.