Probing student understanding of total internal reflection and optical fibers using Piaget-style interviews conducted both face-to-face and electronically

1
Probing student understanding of total internal
reflection and optical fibers using Piaget-style
interviews conducted both face-to-face and
electronically DJ Wagner1,2, JJ Rivera1, Fran
Mateycik1, and Sybillyn Jennings3 1Rensselaer
Polytechnic Institute, 2Grove City College,
3Russell Sage College
The Context
The Science of Information Technology (ScIT)
introduces students of all majors to the
physical principles behind the operation of
information systems. NSF is supporting current
efforts to make ScIT materials useful to a large
audience. As part of that effort, we are
designing diagnostic questions addressing the
topics covered in ScIT. Diagnostic questions are
most useful when they address student
preconceptions and distinguish between different
cognitive models 1. Clinical Interviews have
long been regarded as an effective means of
eliciting students conceptual frameworks 1-3.
Piaget 3 developed the method of critical
exploration to see what thoughts lay behind a
childs initial answer to a question, and the PER
community has used this method extensively
1-2. We used Piaget-style interviews to study
students understanding of total internal
reflection (TIR) and how TIR relates to the
operation of optical fibers.
Photograph of Optical Fiber next to sewing
needle. The core of the fiber is 62 microns in
diameter the cladding is 125 microns.
Organization and Status of Materials
The Study

• What is an optical fiber and what does it do?
• Follow-up questions included How does the fiber
  keep the light from escaping? and What can you
  tell me about refraction?

Grey Not Available Red Original Format Yellow
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2 Physics Faculty

• Faculty, REU students, and in-service
  (non-physics) teachers were interviewed in a
  traditional (face-to-face) form in the Summer of
  2002.
• ScIT students (both pre- and post-instruction)
  were interviewed via WebCTs Chat Room in the
  Spring of 2003.

5 Physics Students (REU)
5 In-Service Teachers
Materials located at http//www.rpi.edu/dept/phys/
ScIT
22 ScIT Pre-Instruction
8 ScIT Post-Instruction
Conclusions about Mental Models
Demographics of Interviewees
We identified the following 7 stages of cognitive
understanding, based on the interview responses.
Most stages were seen in e-interviews as well as
face-to-face interviews.
Conclusions about Interview Formats
Novice

• E-interviews can provide valuable information
  about cognitive
• models. They provide some advantages over
  face-to-face interviews but have their own set of
  limitations.
• Instructor time is smaller in e-interviews, due
  to decrease in transcription time student time
  is greater in e-interviews.
• Several students called the e-interview fun or
  interesting

No concept of light carrying signal
Light just needs to be contained (by, e.g., dark
coating)
Comparing E-Interviews with Traditional Face-to-Face Interviews Comparing E-Interviews with Traditional Face-to-Face Interviews
Advantages of E-Interviews Disadvantages of E-Interviews
Minimal transcription needed!!! (WebCT records conversations in Chat Rooms 1-4.) Can be conducted from wherever, whenever, and however is convenient (at home, listening to music, eating ice cream, in jammies, etc.). Can hold 2 or 3 interviews simultaneously, typing questions for student 3 while students 1 and 2 are typing their responses. (4 at a time is a bit much.) Typed thoughts often come across more coherently than spoken thoughts. Apparent anonymity lets students express their lack of knowledge with less embarrassment. Slowness of typing (vs. speech) results in longer time to gain comparable amount of data the median time for an e-interview was 5 times the median for face-to-face interviews. Less personal connection between interviewer and interviewee cant read body language must establish rapport over distance. Students might be multitasking too not quite a controlled environment. Student cannot draw difficult for instructor to provide images. Some students may be uncomfortable using Chat Room to communicate.
Fibers use mirrored surface or other
non-refractive reflection
Use phrase Total Internal Reflection
Recognize that fibers work through refractive
effect
Can explain TIR in terms of Snells Law
Laser light trapped in a plastic fiber. Air
serves as the cladding.
Can explain TIR to someone who doesnt know what
a sine function is.
Expert
1 Lillian C. McDermott, Bridging the Gap
Between Teaching and Learning The Role of
Research, The Changing Role of Physics
Departments in Modern Universities Proceedings
of ICUPE, ed. by E. F. Redish and J.S.
Rigden. 2 E. Hunt and J. Minstrell, A
Cognitive Approach to the Teaching of Physics,
Classroom Lessons Integrating Cognitive Theory
and Classroom Practice, ed. by McGilly (MIT
Press, 1994). 3 J. Piaget, The childs
conception of the world, trans. by J. A.
Tomlinson. (Littlefield, NJ, 1926/1972).
RPI work supported in part by NSF CCLI Program
under grant DUE-0089399. Thanks as well to Leo
Schowalter for access to ScIT students, and to
the rest of the ScIT advisory committee Karen
Cummings, Toh-Ming Lu, Saroj Nayak, Jim
Napolitano, Peter Persans, and Wayne Roberge.