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

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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

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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.