Lecture Demonstrations in Modern Physics: Quality vs. Quantity Homeyra Sadaghiani and Lei Bao Physics Department, The Ohio State University, 174 W. 18th Ave. Columbus, OH 43210 [email protected] In a study conducted in modern 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 modern 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. 1. Introduction encourage students to think about the physics of the problem. In addition, some teachers claim The findings of pedagogical research often demonstrations help students develop an intuitive favor the use of in-class demonstrations, and these feeling for the real world and can translate abstract demonstrations are becoming more common in ideas into a concrete and practical form. [1, 5] introductory physics courses. In large universities, A significant part of early studies on lecture easy access to a wide variety of demonstrations demonstrations focused on macroscopic topics with professional technical support and the such as Newtonian mechanics; very little work has popularity of demonstrations with students (from been done in the microscopic domain of modern course evaluations), encourage instructors to fill physics, where the macroscopic observation of their lectures with a large number of physical events is not enough to understand the demonstrations. processes that cause the final results. Early findings in pedagogical research often This study evolved during another modern favored the use of lecture demonstrations without physics research project.[7] The researcher, who many constraints and focused on causing more attended lectures for two modern physics classes excitement and producing “oohs” and “ahs” from observed an interesting result when analyzing students.[1,2] However, later studies indicate that students’ responses to the end-of-quarter surveys. the effectiveness of these demonstrations in Here we share these results, using examples of enhancement of learning strongly depends on the demonstrations on the photoelectric effect. degree of students’ interaction and 2. Research Methods involvement.[3] In most studies, the evaluations of lecture Our research methods in this study include demonstrations in physics class often rely mostly three approaches: class observations, an in-class on the students’ positive comments about these response system, and on-line surveys. demonstrations.[4] In fact, one of the most 2.1. Class Observations: important arguments in favor of in-class demonstrations in the literature of physics We observed every lecture throughout the ten- education is the overwhelming positive comments week quarter for two calculus-based modern on course evaluations. They indicate that physics classes at The Ohio State University and demonstrations are fun and exciting, making the paid close attention to students’ attitudes and lecture less dull and boring. [5, 6] behaviors and the lecture material. We took Furthermore, some physics teachers argue that detailed notes related to student learning processes lecture demonstrations can lead to a better and behaviors in class to see how these related to understanding of physics concepts and can class survey results. Lectures met three times a week, each for 48 students to participate in two online surveys. minutes. In addition, there were two recitations Students were told that their responses would be per week and seven laboratory sessions during the appreciated in helping with research and that the quarter. The lecture covered the topics of waves questions were ungraded and voluntary. (four weeks), geometrical optics (one week), The first survey was given in the seventh week interference and diffraction (one and a half of the quarter, and the second one during the last weeks), relativity (one and a half weeks), and week. Both contained multiple-choice and open introduction to quantum mechanics (two weeks). ended questions, mostly on the physics content Each class had about 45-50 attendants who were from the lectures. Since this was a voluntary task, scattered mostly at the back of a large classroom. only 57 (out of 112) students took the first survey The lecturer for both classes was a condensed and 69 students took the second one. matter experimental physicist, who, although an 3. Results experienced instructor, was teaching the modern physics class for the first time. His overall method Our observations indicate that the lecturer was was a traditional lecture; however, he included as knowledgeable about the content of the course and many demonstrations as possible in the 48 minutes had organized the topics and material well. The of each lecture. Some lectures had up to three or variety of different materials being used during the four demonstrations in addition to slides, lecture would seem impressive to an observer at simulations, and/or short video clips. the beginning. However, very little time was spent During the demonstrations, the instructor on explaining each demonstration and, more rarely asked questions, and of the questions he importantly, its connection with the physics asked, most were rhetorical or were answered by concepts intended to be taught. The instructor did the instructor before giving enough time for not seem to be concerned with the students’ students to explore their thoughts and to respond. engagement and did not ask students to make Students’ questions, if any, were limited to the end predictions about the experiments or any other of class. questions before or after the demonstrations. Therefore, the variety of demonstrations often did 2.2. In-Class Response System not attract students’ attention. At the beginning of the quarter, the instructor The use of the voting machine in the first few tried to use multiple-choice and short answer weeks of the quarter created some engagement on questions to get student feedback through a the students’ part. This tool might have provided computerized voting machine.[8] This in-class valuable feedback to the instructor if it was used response system served as both a research and an throughout the quarter. When the instructor assessment tool. We divided students into groups stopped using the voting machine in lecture, there of four.[9] Each group obtained a remote was no effective assessment of the students’ answering device to participate in in-class polling. learning and understanding of the concepts during After a few weeks, however, the instructor the lecture. (See Ref. 8) realized that the in-class response system did not The results of our on-line surveys confirm that give him enough time for all the demonstrations he students had very little to take home from all the had planned for the class. As a result, he stopped demonstrations they had observed in the class; and using the voting machine, and therefore, all they could remember were parts of an eliminated much of the feedback that he could get observation or fragments of a concept. For from the students during the class period. example, there was a demonstration in class on the topic of the photoelectric effect. The apparatus 2.3. Survey Questions consisted of an ultraviolet light shining on a The primary research methods were the voting negatively charged electroscope with a piece of machine and the class observations. However, metal attached to the top. Students had observed when the instructor stopped using the in-class that the leaves of the electroscope moved close response system, we replaced it with on-line together when an ultraviolet light was shone on the surveys to get feedback and collect data for our electroscope. Furthermore, the instructor had research. We asked 112 freshman engineering explained that the photons from the light can transfer enough energy to the electron in the metal and remove the electron from an atom in the metal. By removing the electrons, the electroscope would be discharged. In the second survey we had two questions on this topic. In the first question, we explained the exact setting of the demonstration explained above. Then we asked students to recall what Incorrect Confused Incomplete Correct happened when the instructor shined the light on the negatively charged electroscope and to explain Figure-1. Results of a survey question on what happened and why. The point was to see if effectiveness of an in-class demonstration. students could recall anything from this The results of the second question were not experiment, and also to remind students of the any better. More than 37% of the students stated experiment's setting so that we could ask a second that they did not know the answer, 13% confused question. This question asked students to predict this with demonstrations on light interference, and what would happen if the electroscope was 31% answered incorrectly (see Figure-2). charged positively. The students had not seen the results of shining the UV light on a positively charged electroscope in the class. Therefore, we were trying to see if these students could transfer any learned knowledge from one demonstration to a different but related context. We had expected that most students at least would answer the "what happened" part of the question correctly, even if they could not give a clear explanation for the "why" part of it. To our Dont know Incorrect Confused Incomplete Correct surprise, more than 42% of the 69 students Figure-2. Results of a survey question on transfer of surveyed did not even remember the experiment. in-class demonstration. Approximately 23% of the students confused this Below we include several students' statements experiment with many other ones they had seen to show details of their confusions.