Improving secondary students’ scientific literacy and
interviews. Generally, the participation to the Project was considered by the teachers as an opportunity for addressing content knowledge related issues and for implementing new pedagogical methods. In 2010 the PLS has become a National Plan, and its impact is increased in terms of schools involved.
The PLS-Physics has emphasized the teaching of aspects of Nature of Science as scientific inquiry (Bybee, 2006;
Krajicik et. al., 2000; Schwartz & Crawford, 2006) and mathematical modelling (Lijnse, 2008). The proposed activities were mainly laboratory experiments (lab-work), in which students could improve their competencies in data collection and analysis in order to construct a scientific model of the observed phenomena. The lab-work aimed also at improving students’ critical reasoning and argumentation skills, and at providing opportunities for self-assessment about basic physics for those students willing to enrol in a University physics degree. During the lab-work, the teachers were helped to organize and design teaching materials to be transferred in their classroom practice; the experiments being carried out both at University and schools. In the latter case, the aim was also to help in including experiments in the physics school curriculum.
In the following, the description of the PLS-Physics activities implemented in the last two years at the Department of Physics of the University of Naples “Federico II” is reported.
ACTIVITIES OF THE PLS PHYSICS - NAPLES IN 2010-12 SCHOOL YEARS
In 2010-11 five schools, eight teachers and about 80 students have been involved for a total of 100 hours of activities, both at school and University laboratories. In 2011-12 eight schools, ten teachers and about 107 students participated to the project, for a total of 150 hours of activities. Each school implemented the activities for about 20 hours. The laboratory experiments integrated traditional measurement apparatuses, real-time data collection and simulation tasks. Content areas addressed were: mechanics, thermal phenomena, optics, electric circuits. The organization of the activities is shown in Figure 1.
Figure 1. Structure of the activities carried out in the PLS – Physics, 2010-11 and 2011-12
The first activity (4h) helped the students familiarise with: scientific notation, rules for significant figures, uncertainties and their propagation, data fitting and simple mathematical modelling. The second and third activities (2 x 4 hours) have proposed two experiments chosen by the school teachers and University researchers amongst those carried out in the laboratory courses of the first two years of the Physics degree (e.g., measurement of the elastic constant of a metallic spring via oscillation period and Hooke’
law; measurement of gravity acceleration using a simple pendulum; study of the temperature vs. time trend of a hot-water mass cooling in a constant temperature environment; measurement of an unknown electric resistance). The fourth activity, at the Department of Physics, concerned the measurement of : - electron charge to mass ratio by magnetic deflection of an electrons’ beam across Lorentz’ coils, or - human hair thickness using the diffraction pattern of a laser beam. During all lab-work, students in small groups (4-5) carried out measurements and data analysis. For instance, in one activity, the students
measured the temperature T(t) of a hot water mass, initially at T0 ,as it cools down in the environment at constant Ta (Figure 2, left). The data are modelled by ( )
, min. T T
T t T
e 20
a
a t
0− ,
− = −x x (Figure 2, right). In another activity, the students estimated the unknown resistance of a resistor Rx using a two-resistor series circuit, given the voltage of a battery , and measuring ∆VR1 across the known variable resistor R1 (Figure 3, left). The circuit behaviour is modelled by VV
R 1 R R
x
1 1
T
T = + , (Figure 3, right).
Figure 2. Students at work during the PLS-Physics water cooling activity. Data analysis at right.
Figure 3. A student measures the voltage in the two-resistor series circuit activity. Data analysis at right.
At the end of the school year, during a workshop organized at the University, selected groups of students presented, in about ten minutes, one of the experiments carried out; all the participating students and their teachers were invited to this workshop. Finally, the involved teachers presented two seminars to other colleagues about their own experience in PLS, in order to share opinions and to propose ideas for improving students’ participation.
EXAMPLES OF TEACHING-LEARNING SEQUENCES IMPLEMENTED IN PLS PHYSICS-NAPLES
Here some details on emblematic activities of the PLS-Physics. These activities present a coherent teaching- learning sequence on a specific theme/context for the physics contents addressed. Methodologically the sequence is inspired by an integrated Inquiry-Based Learning and Design-Based Learning approach (Fortus et al., 2004; Puntambekar & Kolodner, 2005; Schnittka & Bell, 2010). Two addressed themes: optical fibres (emphasis on refraction and reflection law, index of refraction) and thermal insulation (Newton’s law for cooling/heating of fluids). As for the other PLS laboratory activities, a Preliminary Session (about 3 hours), was devoted to familiarise the students with the basic elements of uncertainties, significant figures, scientific notation and data fitting. Moreover, the students were introduced to some software packages used in the activities (Logger Pro, Microsoft Excel and Cabrì Géomètre).
Optical fibres
This sequence has involved 23 students at the school laboratory of a Scientific Lyceum in Naples. The lab- work has been integrated by activities with Cabrì Géomètre aimed at carrying out accurate measurements and building effective descriptive models of phenomena (e.g., when a trajectory is visible and an image is produced via a digital camera) (Monroy, Lombardi & Testa, 2008; Testa & Lombardi, 2007).
In the first meeting (3 hours) after the Preliminary Session, some situations related to the use of optical fibres in telecommunications have been discussed. Then, the behaviour of fibre glass lamps, plastic rods, glass rods interacting with light was investigated in order to find out similarities and differences between optical fibres and other transparent objects that may guide the light. Then, an intriguing experiment with an illuminated water jet was performed by the students in small groups in order to discuss about how to build a light guide (Figure 4). The analysis of this experiment allowed to address the behaviour of light when it travels in homogenous materials and encounters interfaces between them.
Figure 4. Optical fibres sequence: propagation of light in a water jet
Later, the students observed the path of a laser beam in a tank half-filled with water by mean of diffusing particles. Students’ attention was focused on both the phenomena of reflection and refraction, as ways to deviate the light from a rectilinear path (Figure 5).
Figure 5. Optical fibres sequence: propagation of light in a water tank
In the second meeting (3 hours), refraction and reflection were formalised (Figures 6 and 7) through the Snell’s laws by using Cabrì Géomètre. The index of refraction of an homogenous medium with respect to another was also introduced as the optical property which allows to predict the light path deviation when light hits the interface between the two media. The reflection law was introduced to quantitatively describe what happens when total reflection conditions are met. By means of a Cabrì applet, the students explored light propagation in diverse media, e.g., from more to less refractive ones, and investigate the conditions under which total internal reflection occurs.
Figure 6. Optical fibres sequence: measurement of incident and refraction angles
Figure 7. Optical fibres sequence: measurement of incident and reflection angles in the case of total reflection
The third and final meeting (3 hours) proposed a qualitative experiment about the propagation of a laser beam in a glass tube immersed in air and in water to observe how an optical fibre is made; in particular, to clarify the need of a cladding to “protect” the fibre core, and its influence on light propagation in the fibre and acceptance angle. The regularities observed were transformed in some rules by means of Cabrì simulations (Figure 8).
Figure 8: Optical fibres sequence: simulation of an optical fiber with Cabrì
The proposed simulation allowed to: - introduce acceptance angle, numerical aperture and critical angle at which total internal reflection within the core occurs; - relate the numerical aperture to the refractive indices of core and cladding in a step-index optical fibre.
Thermal insulation
This teaching-learning sequence has involved 15 students at the school laboratory of a Technical Vocational School in Naples. The lab-work has used real-time measurement and temperature probes built up by the students.
In the first meeting (4 hours) after the Preliminary Session, the students in small groups (3-4), measured, first with a Hg thermometer and then with an on-line temperature probe, the change of temperature with time of water masses in a plastic cup (initial T = 60° C, left to cool down in a quasi-constant temperature laboratory, about 23°C). Each measurement lasted about 20 minutes. The students studied the collected data, modelled their trend by an exponential function, derived and compared the time constant of the cooling process in both thermometer and temperature probe experiments (Figure 9 and 10). At the end, the students related the parameters of the modelling exponential function to the physical variables of the experiment (mass of the water, heat capacity, material of the cup, heat exchange surface, etc…). Results of fit analysis for the data in Figure 9 and 10 are reported in Table 1. The values of the fit parameters in the two experiments are comparable.
Figure 9. Thermal insulation sequence: data analysis of the water cooling experiment with a thermometer.
Figure 10. Thermal insulation sequence: data analysis of the water cooling experiment with a temperature probe.
Table 1. Parameters of the water cooling modelling function T t( )=Ae−Ct+B
A(°C) B(°C) C(10− −5 1s )
Hg Thermometer ( .20 0 0 4! . ) ( .28 9 0 4! . ) (62 2! )
Temperature probe ( .20 97 0 03! . ) ( .28 82 0 03! . ) ( .61 8 0 1! . ) In between the first and third meeting, the students constructed, with the Electronics Systems teacher and as part of their school syllabus, three temperature sensor circuits, using the integrated component LM35C. In the second meeting (4 hours) the students addressed the problem of choosing the most suitable materials for the walls of a house so that each room could be at a constant temperature of about 22°C when lighted up by the Sun. Each group discussed possible solutions to the problem and proposed their ideas to the whole class. After sharing the students’ proposals, it was agreed to build up a cardboard house with three “rooms”, each equipped with one of the previously constructed temperature sensor circuit.
In the third and final meeting (4 hours), the students built the agreed prototype (Figure 11 and 12) and tested it by changing the materials of the “walls” in order to keep a constant temperature in the rooms when the house was illuminated by an “artificial” Sun, i.e. a 150 W lamp.
Figure 11. Thermal insulation sequence: a cardboard “house”. The fan cools down one of the “rooms”
Figure 12. Thermal insulation sequence: temperature sensor circuit designed and built by the students, in a room of the “house”
The students drew upon the previous experiments on the cooling of water to reflect upon how the cup material influenced the temperature trend of the water. Moreover, they explored different materials and conditions to address the problem of insulation and investigated how a polystyrene “ceiling” affected the temperature of room “1” with respect to rooms “2” and “3” without ceiling. Room “2” was the farthest from the lamp, room “3” was illuminated as room “1” (Figure 13 and 14).
Figure 13. Thermal insulation sequence: test of the effect of a material. Room 1 is covered by a polystyrene
“ceiling”, the others are uncovered. The “house” is illuminated by a 150 W lamp (the “Sun”).
Figure 14. Thermal insulation sequence: real-time measurements of the temperature in the three rooms of the “house” illuminated by a 150 Watt lamp (see Figure 13).
The data analysis shows that in room “2” temperature (blue data) was almost constant:T2( .23 02 0 09! . )cC . Fit parameters for rooms “1” and “3” temperature are reported in Table 2. The time constant for room
“1” is (357 4! )s while for room “3” it is (111 3 10! )) s.The different time constants are due to the polystyrene “ceiling”.
Table 2. House heating modelling function T t
( )
=A(
1−e−Ct)
+B (see Figure 14)A(°C) B(°C) C()10− −5 1s )
Room 1 (red) ( .5 16 0 03! . ) ( .22 26 0 04! . ) (280 3! ) Room 3 (green) ( .2 47 0 02! . ) ( .22 62 0 02! . ) (90 3! )