METHODOLOGICAL APPROACH TO MODERN PHYSICS EXPERIMENTS. Luka Mandić, Department of Physics and Ecology, Technical Faculty, Rijeka, Croatia

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1 METHODOLOGICAL APPROACH TO MODERN PHYSICS EXPERIMENTS Luka Mandić, Department of Physics and Ecology, Technical Faculty, Rijeka, Croatia Dubravka Kotnik-Karuza, Mariza Sarta-Deković, Physics Department, Faculty of Philosophy, Rijeka, Croatia Abstract The role of experimental approach in studying physics has proved its value in different fields of physics and at all teaching levels. We have analysed the contents of physics textbooks intended for the fourth year of learning physics in secondary grammar schools in Croatia which cover practically all subjects of modern physics in a very concise, mostly descriptive way. Faced with the problem how to train our students to transmit the knowledge and understanding of concepts and ideas of modern physics to their pupils in the most effective way we have proposed a relatively simple set of experiments dealing with the physical structure of matter to be introduced in the last year of the undergraduate university courses. These experiments, conducted by the students individually, should make phenomena on the microscopic scale more accessible to them, give them an opportunity to consolidate their elementary knowledge of physics and provide them with the only and probably last opportunity to engage in a process of investigation and to learn the methodology of scientific research. Introduction An important problem of physics learning lies in the linking of physical quantities and phenomena in order to build models and concepts. According to the constructivistic theory one of the most efficient methods of active acquirement of knowledge is experiment: demonstrative in the initial and laboratory work in the advanced phase of modelling [1-2]. Assuming that understanding of physics depends on the degree of implementation of experiments in physics teaching at all levels, from the very beginning up to the professional [3], we propose a set of experiments which, penetrating in the structure of matter on microscopic scale, contribute to a better understanding of modern physics. These experiments are: Zeeman effect, Compton effect, Franck-Hertz experiment, Moseley's law and Hall effect. Our work takes place in the Physics Department located at the Faculty of Philosophy in Rijeka, Croatia. For the first time in a 40 years long tradition our institution has such sophisticated laboratory equipment and now we get a chance to raise the quality of our present and future physics teachers on a higher level. Motivation We interviewed some young physics teachers and research assistants. They represent a significant source of information because of their fresh experience in being excellent students, teachers and scientists, at the high school and university. They support the idea that without such experiments a newly graduated physics teacher is not capable to create clear ideas in the students' minds, which are adaptable to the lower level of mathematical and physical comprehension in the high school [4]. Maybe the teacher also has his own misconceptions.

2 The lectures on modern physics are mainly presented in the fourth year of the high school. Hence the time given is fairly short. In spite of extensive schoolbooks, teaching about this issue is very poor. The pupils neither see nor feel anything but statements on the blackboard, which is pretty far from real understanding. In order to pass exams, the pupils have to learn by heart to acquire knowledge of the lowest degree, without any systematic concept. The first part of our motivation has a subjective character, because it consists of individual opinions, but the second part is very objective. We have analysed the contents of physics textbooks intended for the fourth year of learning physics in the high schools in Croatia, which cover practically all subjects of modern physics [5]. The results of this investigation are given in Figure 1. We have found them extremely rich in subjects covering different fields of modern physics and divided in obligatory, extended and facultative parts. However, the subject matter is given in a very concise, mostly descriptive way. Such books are useless to the pupils without a skilled teacher as a mediator able to choose from offered materials, to reduce or to give a detailed explanation [6]. Such high level skills may be gained only by use of methodical experiments, which should become unavoidable components of the teachers' education.

3 Franck -Hertz experiment particle nature of light - pho ton emission quantum o f energy radiation excitation energy valence electrons quantum transitions collisions - elastic, inelastic gas filled tube Compton effect radioactivity EM spectrum - gamma radiation isotopes matter waves dual nature of light de Broglie wavelength scattering energy and angular momentum conservation lows Compton wavelength Mossbauer effect Zeeman effect atomic models quantisation of energy quantum numbers of electrons states EM spectrum - visible radiation interference, polarisation electron spin magnetic properties of atom angular momentum many electrons atom degenerate energy levels energy level splitting selection rules Bohr's magneton Fabry-Perot interferometer Moseley's low and X-rays fluorescence atomic energy levels atomic radiation photoelectric effect emission line spectrum excitation, ionisation EM spectrum - X-ray radiation binding energy Rydberg's constant characteristic X-ray radiation collisions bremsstrahlung (retarded radiation) Coulomb potential energy fluorescence charge screening Hall effect semiconductors - intrinsic, extrinsic electrons, holes conductivity of semiconductors band theory forbidden zone valence band conduction band mobility of the charge carriers magnetic resistance Hall coefficient Hall voltage Number Number of textbooks of textbooks Figure 1. Physical quantities and phenomena included in the proposed experiments and their appearance in the investigated sample of high school textbooks in Croatia

4 Experiments The experimental set ups of our experiments are shown in Figure 2. a) Compton effect b) Franck Hertz experiment c) Hall effect d) Moseley's law e) Zeeman effect Figure 2. Set up of modern physics experiments The importance of these experiments in physics teachers' education can be summarized in the following way. General characteristics: In conceptual sense complex phenomena are represented by relatively simple experimental set ups Their subjects correspond to the subjects of investigated schoolbooks Measurements are reproducible Numerical results are comparable with theoretically known physical quantities

5 Role of the experiments: To enable better understanding of physics theory To develop creativity by active learning To shed light on the microscopic scale of phenomena that are unavailable to usual everyday perception To repeat and to confirm elementary knowledge of physics To help the construction of new physical models using the simplest possible mathematical formalism To make creating models and concepts necessary for teaching practice easier To make future teachers able to adapt the interpretation of results to different levels of pupils' comprehension To give the university students of teachers' courses the only and probably last chance of insight in the scientific methodology of natural sciences based on active relations between theory and experiment [7-8]. Application In the education of physics students (teachers' and engineering courses): establishing new experimental courses In the professional and scientific development of postgraduate students in educational physics In the permanent education of physics teachers In work with talented pupils: final works or competitive works. Conclusion Quantities and phenomena related to the structure of matter belong to different branches of modern physics. Their comprehension is difficult not only because they are out of reach of our macroscopic perception but also because their exact description requires a complex mathematical formalism. Thus, penetration in the microscopic world by an experiment, which includes and connects numerous relevant quantities, stimulates model building and creates clear ideas at different levels of mathematical and physical comprehension. The suggested experimental course of modern physics is of extraordinary importance for future physics teachers. In the frame of undergraduate and postgraduate level it represents a unique possibility of direct observations of the microscopic phenomena, facilitating the creation of concepts and models unavoidable in teachers' praxis. Such experiments inaugurate the scientific methodology of natural sciences as an imperative in education at any level and are expected to influence the quality of physics teaching in general. Our set of experiments represents an optimal relation between the conceptual completeness and its price, which is especially important in developing countries.

6 References [1] Kotnik-Karuza D and Milotić B 1996 The role of experimental work in physics education Situation at the universities in Croatia EPS 10 Trends in Physics (Sevilla) pp 157 [2] Van Driel I and Verloop N 1999 Teachers' knowledge of models and modelling in science Int. J. Sci. Educ. 21 (11) [3] White R T 1996 The link between the laboratory and learning Int.J.Sci.Educ. 18 (7) [4] Gayle N 2001 A report of undergraduates' bonding misconceptions Int.J.Sci.Educ. 23 (7) [5] Kotnik-Karuza D, Mandić L and Sarta-Deković M 2003 Metodičko oblikovanje eksperimenta u modernoj fizici Problemski i istraživački usmjerena nastava fizike (Split) pp [6] Hodson D 1996 Practical work in school science: exploring some directions for change Int.J.Sci.Educ. 18 (7) [7] Melear C T 1999 Middle and secondary science teacher opinions about working in scientists' laboratories during preservice preparation EJSE 4 (2) [8] Gott R and Duggan S 1996 Practical work: its role in the understanding of evidence in science Int.J.Sci.Educ. 18 (7)