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Why we should teach the Bohr model and how to teach it effectively. Sam McKagan, Kathy Perkins, Carl Wieman University of Colorado July 30, 2007. Faculty: Michael Dubson Noah Finkelstein Valerie Otero Kathy Perkins Steven Pollock Carl Wieman Joe Redish (visiting)

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Why we should teach the Bohr model and how to teach it effectively

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Why we should teach the bohr model and how to teach it effectively l.jpg

Why we should teach the Bohr model and how to teach it effectively

Sam McKagan,

Kathy Perkins, Carl Wieman

University of Colorado

July 30, 2007


Acknowledgements l.jpg

Faculty:

Michael Dubson

Noah Finkelstein

Valerie Otero

Kathy Perkins

Steven Pollock

Carl Wieman

Joe Redish (visiting)

Programmers:

Chris Malley

Sam Reid

Ron Lemaster

John deGoes

Postdocs:

Sam McKagan

Linda Koch

Grad Students:

Wendy Adams

Jack Barbera

Chris Keller

Pat Kohl

Noah Podolefsky

Chandra Turpen

Danielle Harlow

Kara Gray

Charlie Baily*

Acknowledgements


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Why teach atomic models?

Content: Understanding atoms crucial for understanding basis of modern technology.

Beliefs: Students can appreciate the beauty of the universe by understanding the fundamental building blocks of nature.

Skills: Good example of model building – can be used to teach scientific reasoning skills.

Relevant at all levels of education

– grade school to grad school


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Controversy – how to teach atoms

  • Researchers* claim that learning the Bohr model is an obstacle to learning true quantum nature of atoms. Should avoid teaching Bohr model entirely.

  • Many in PER take this idea seriously – incorporate into curriculum design.

  • Area of active debate among high school teachers.

*Fischler and Lichtfeld, “Learning quantum mechanics,” in Research in Physics Learning: Theoretical Issues and Empirical Studies (1992), pp. 240-258.

Fischler and Lichtfeld, “Modern physics and students’ conceptions,” Int. J. Sci. Educ. 14, 181-190 (1992)


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Several Objections

  • Research poorly conducted.

  • Assumption that Schrodinger is only goal.

  • Practicing scientists use the Bohr model!

  • Bohr model taught in high school.

  • Research shows that avoiding discussions of misconceptions doesn’t work. Must explicitly address them!


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Design a study to answer this question:

  • Is teaching the Bohr model an obstacle to learning Schrodinger model of atom?

    Method:

  • Can’t do a controlled study because no one will teach course without Bohr model.

  • Can we develop a curriculum focused on model-building, including treatment of Bohr model, that leads students to develop understanding of Schrodinger model of atom?


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Real World Examples:PMTs, discharge lamps, fluorescent lights, lasers, alpha decay, STMs, LEDs, CCDs, MRIs, BEC

Model Building:Why do we believe this stuff?

Reasoning Development:How do we make inferences from observations?

Memorization

Physics 2130

Modern Physics for Engineering Majors

~200 students

Interactive simulations

Peer Instruction

Solving complex 3D

Schrodinger problems

Special Relativity

Collaborative Homework sessions


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Instruction on Atomic Models

  • Lectures: focus on model-building, reasons for each model.

  • Homework: compare and contrast models, discuss the advantages and limitations of each.


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Models of the Atom

  • Democritus – Billiard Ball (450 BC)

    • Why? Smallest indivisible chunk of matter

    • Problem: Atoms can be ionized.

  • Thomson – Plum Pudding (1904)

    • Why? Known that negative charges can be removed.

    • Problem: Rutherford showed positive charge was small core.

  • Rutherford – Solar System (1911)

    • Why? Scattering showed small core.

    • Problem: electrons should spiral into nucleus in ~10-15 sec.

  • Bohr – fixed energy levels (1913)

    • Why? Explains spectral lines.

    • Problem: No reason for fixed energy levels

  • deBroglie – electron standing waves (1924)

    • Why? Explains fixed energy levels

    • Problem: still only works for Hydrogen.

  • Schrodinger – quantum wave functions (1926)

    • Why? Explains everything!

    • Problem: hard to understand


Results l.jpg

Results

  • Essay question on final exam: “Use words, graphs, and diagrams to describe the structure of a Hydrogen atom in its lowest energy state .”

  • Question does not mention models. Which model(s) do students use?

  • Analyze responses from random sample of 50 students from each class.


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Multiple Models

Models used to describe Hydrogen atom

One Model

Summary:

  • More students are using Schrodinger model than Bohr model, BUT…

  • About 1/4 still use Bohr model only.

  • Only about 2/3 use Schrodinger model at all!

    We want to do better!

100%

90%

80%

70%

60%

Percentage of Students

50%

40%

30%

20%

10%

0%

Bohr

deBroglie

Schrodinger

Bohr

deBroglie

Schrodinger

Fall 05 Spring 06


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Review Curriculum

Topics

  • Models of the atom through deBroglie

  • Electron waves

  • Schrodinger Equation

  • Other applications of Schrodinger Equation

  • Schrodinger model of atom

Not enough explicit connections!

~ 5 weeks

Redesign Curriculum: Add focus on connections between Schrodinger model and other models, model-building exercise.


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Redesign Curriculum

Fall 06:

  • Add focus on connections between Schrodinger model and other models.

  • Add general model building exercise.

    Spring 07:

  • Add interactive computer simulations:

    • Models of the Hydrogen Atom*

    • Rutherford Scattering*

  • In homework, students work through sims, describe reasons for adopting each new model.

*http://phet.colorado.edu


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http://phet.colorado.edu


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Multiple Models

Models used to describe Hydrogen atom

One Model

Summary:

  • ~80% of students use Schrodinger model.

  • Only ~10% use Bohr model alone.

     Teaching Bohr model does not prevent students from learning Schrodinger model.

100%

New Curriculum

Old Curriculum

90%

+sim

80%

70%

60%

Percentage of Students

50%

40%

30%

20%

10%

0%

Bohr

deBroglie

Schrodinger

Bohr

deBroglie

Schrodinger

Bohr

deBroglie

Schrodinger

Bohr

deBroglie

Schrodinger

Fall 05 Spring 06 Fall 06 Spring 07


Further results l.jpg

Further results…


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For more info…

See our article at:

http://arxiv.org/abs/0707.1541

Download simulations (free!) from PhET website:

http://phet.colorado.edu

Course materials (lecture notes, homework, exams) available at:

http://per.colorado.edu/modern


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