Framework for using modern devices in an introductory physics
course
SEEMPE 2015 PEF UL, Ljubljana 2-3.2.2015
Eugenia Etkina Graduate School of Education,
Rutgers University USA
Gorazd Planinšič Faculty for Mathematics and Physics
University of Ljubljana, Slovenia
How to integrate modern topics (devices, concepts…) into physics curriculum ?
• 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 ?
Most of the approaches focus on the following questions:
• 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…) •…….
Only few examples:
How to integrate modern topics (devices, concepts…) into physics curriculum -
- without loosing the coherence of the curriculum and without overloading it?
But we will focus on a different aspect of the question:
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.
DEVICE
Using X as a black box
X
Learning how X works
Learning new physics using knowledge of how X works
G. Planinšič, E. Etkina, TPT, 52 (2014) 94-99.
Let’s see how this works for a
light emmitting diode (LED)
Using LED as a black box
E. Etkina, G. Planinšič, Physics World (March 2014) 48-51.
Recording and analyzing motion using blinking LED and long-time exposure photos
LED Bulb Switch
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?
Learning how an LED works
“Physical experiences and images are required in order to understand anything at all.”*
*J Zull, The art of changing the brain, 2002
• Physical experience • Images • Inventing ideas and testing them • …. and only THAN “Time for telling”
Similarities and differences between a light bulb (known) and an LED unknown)
E. Etkina, G. Planinšič, TPT 52 (2014) 212-218.
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
+ 3.0 V GLOWS GLOWS
Measuring I-U dependence – quantitative investigation
-200
-150
-100
-50
0
50
100
150
200
-3 -1 1 3
I(mA)
U(V) 0
2
4
6
8
10
12
14
16
18
-3 -1 1 3
I(mA)
U(V)
Light bulb LED
Close view images
“I can see a small (glowing) wire.”
“I can see … nothing.”
Observing an LED under microscope – more images
The teacher can stop here, but if time permits she can proceed with “telling” combined with analogies and kinaestetic activities.
Learning new physics using knowledge of how LEDs work
Students have learned: • I-U characteristic of LED • Colour mixing rules • Wave optics, spectrum
Learning new physics using knowledge of how LEDs work
White LED
G. Planinšič, E. Etkina, TPT (2015) in press.
• 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
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)
• 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
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.
• Design experiments to test the explanations. For each experiment make predictions of the outcome based on each explanation (E1, E2, E3).
Blue LED White LED
Outcome of the testing experiment:
E3: A single LED covered with some material
E1: R,G and B LEDs
E2: Small incandescent light bulb We can not reject E3!
Additional observational experiment: Microscopic observation
Blue LED White LED
OFF
ON
Blue LED
Yellow material
Blue and Yellow light = White light
Improved explanation:
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.
Possible explanations
Observational experiments
Testing experiments
Reflections and revisions
Application
YES
NO
PATTERNS
PREDICTION
PROPOSE DIFFERENT
MORE
More testing experiments
Do outcomes agree with predicitions?
Check assumptions
ISLE cycle
ISLE - Investigative Science Learning Environment E Etkina and A Van Heuvelen, 2001 and 2007
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) 94-99 - (includes 41 references!)
Experiment Questions
Bla
ck b
ox
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].
Describe macroscopically the energy flow and energy conversions in these experiments. Compare and contrast these processes for the two cases.
Ho
w L
ED w
ork
s?
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].
Explain microscopically the energy flow and energy conversions in these experiments. Compare and contrast these processes for the two cases.
New
ph
ysic
s u
sin
g kn
ow
. ab
ou
t LE
Ds
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.
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?
An example of a Unit: Energy
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.
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