Framework for using modern devices in an introductory physics course

Transcription

1 Framework for using modern devices in an introductory physics course Gorazd Planinšič Faculty for Mathematics and Physics University of Ljubljana, Slovenia Eugenia Etkina Graduate School of Education, Rutgers University USA SEEMPE 2015 PEF UL, Ljubljana

2 How to integrate modern topics (devices, concepts ) into physics curriculum?

3 Most of the approaches focus on the following questions: How to explain new physics in a simple/ comprehensible way? How to demonstrate new phenomena? How to motivate/attract /entertain pupils by showing interesting experiments or let them play with them?

4 Only few examples: Liquid crystals (Mojca Čepič) Superconductivity (SPERCOMET, Marisa Michelini ) Basic Quantum mechanics (Dean Zollman, Marisa Michelini ) LEDs (Dean Zollman, James Overhizer ) AFM (Manfred Euler, Ansi Lindel, GP ).

5 But we will focus on a different aspect of the question: How to integrate modern topics (devices, concepts ) into physics curriculum - - without loosing the coherence of the curriculum and without overloading it?

6 Three different ways of utilizing modern devices in an introductory physics course The proposed framework is not meant to be theoretical framework, but rather a guide that will help teachers and educators to think of how to use modern devices in IPCs.

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8 Learning how X works Using X as a black box DEVICE X Learning new physics using knowledge of how X works G. Planinšič, E. Etkina, TPT, 52 (2014)

9 Let s see how this works for a light emmitting diode (LED)

10 Using LED as a black box

11 Recording and analyzing motion using blinking LED and long-time exposure photos E. Etkina, G. Planinšič, Physics World (March 2014)

12 But even black boxes offer opportunities for comparisons and contrasts Why don t we use a small incadenscent light bulb instead of the LED for tracking motion? Switch LED Bulb

13 Learning how an LED works Physical experiences and images are required in order to understand anything at all. * Physical experience Images Inventing ideas and testing them. and only THAN Time for telling *J Zull, The art of changing the brain, 2002

14 Similarities and differences between a light bulb (known) and an LED unknown) E. Etkina, G. Planinšič, TPT 52 (2014)

15 Making it glow qualitative investigation U(V) LED Light bulb -3.0 V Does not glow GLOWS -1.5 V Does not glow Glows 0 V Does not glow Does not glow +1.5 V Does not glow Glows V GLOWS GLOWS

16 Measuring I-U dependence quantitative investigation I(mA) Light bulb U(V) I(mA) LED U(V)

17 Close view images I can see a small (glowing) wire. I can see nothing.

18 Observing an LED under microscope more images

19 The teacher can stop here, but if time permits she can proceed with telling combined with analogies and kinaestetic activities.

20 Learning new physics using knowledge of how LEDs work Students have learned: I-U characteristic of LED Colour mixing rules Wave optics, spectrum

21 Learning new physics using knowledge White LED of how LEDs work Observe spectra of different colour LEDs (R,G,B) using a grating. Identify patterns. Observe spectrum of the white LED using a grating. Identify patterns. Photos of the actual experiment G. Planinšič, E. Etkina, TPT (2015) in press.

22 Propose several mechanisms that could explain how the white LED produces the observed spectrum. E1: R,G and B LEDs E2: Small incandescent light bulb E3: A single colour LED covered with some material that changes the colour of light when the LED light passes through it (if necessary, triggered by a teacher)

23 Design experiments to test the explanations. For each experiment make predictions of the outcome based on each explanation (E1, E2, E3). Testing experiment: Measure I-U curve of the white LED Predictions based on explanations: If E1 than the turn on voltage should be at least 5V (LEDs in series) or 1.5 V (LEDs in parallel) If E2 than the current should flow through the device for any non-zero voltage. If E3 than the I-U curve should be similar to the I-U curve of some monochromatic LED.

24 Outcome of the testing experiment: White LED Blue LED E1: R,G and B LEDs E2: Small incandescent light bulb E3: A single LED covered with some material We can not reject E3!

25 Additional observational experiment: Microscopic observation Blue LED White LED OFF ON

26 Improved explanation: Blue and Yellow light = White light Blue LED Yellow material

27 Testing experiment: Take a blue LED and shine it through a yellow piece of paper. Prediction: We will see white spot where the blue light is shining on the yellow paper. Outcome: shows that only certain type of colour markers produce white colour. Now students have need to know and are ready to learn about FLUORESCENCE.

28 ISLE cycle MORE Observational experiments PATTERNS Reflections and revisions Check assumptions PROPOSE DIFFERENT Possible explanations NO Testing experiments Do outcomes agree with predicitions? YES PREDICTION More testing experiments Application ISLE - Investigative Science Learning Environment E Etkina and A Van Heuvelen, 2001 and 2007

29 Walking through the introductory physics with LEDs 1. Kinematics 2. Energy 3. Electric field 4. DC circuits 5. Capacitors 6. AC circuits 7. Electromagnetic oscillations 8. Geometrical optics 9. Color and wave optics 10. Electromagnetic radiation and photons 11. Semiconductors and p-n junctions 12. Photoelectric effect 13. Nature of light emission, fluorescence and phosphorescence G Planinšič, E Etkina, TPT 52 (2014) (includes 41 references!)

30 New physics using know. about LEDs How LED works? Black box An example of a Unit: Energy Experiment Connect an incandescent light bulb to a battery and observe it glow. Repeat with connecting an LED to a battery and a resistor and observe it glow [5]. Connect an LED to a battery and a resistor and observe it glow. Then take the LED alone and connect it to a voltmeter. Shine white light on it and observe a non-zero voltmeter reading [6]. Connect an LED alone to a voltmeter (use red, green, or blue LED). Shine different color lights on the LED and observe voltmeter reading. The LED produces highest voltage when it is illuminated by light of characteristic wavelength. This potential difference can even power another LED. Questions Describe macroscopically the energy flow and energy conversions in these experiments. Compare and contrast these processes for the two cases. Explain microscopically the energy flow and energy conversions in these experiments. Compare and contrast these processes for the two cases. What are the patterns in your observations? What general rule relating the voltage produced by an LED and the intensity and color of light incident on the LED can you suggest?

31 Summary Two messages that I want to send: Modern devices can be integrated in physics curriculum without overloading it. Students need to practice science process when investigating those devices.