Probing student understanding of total internal reflection
and optical fibers using Piaget-style interviews conducted
both face-to-face and electronically
DJ
1,2
Wagner ,
1Rensselaer
JJ
1
Rivera ,
Fran
Polytechnic Institute,
1
Mateycik ,
2Grove
and Sybillyn
City College,
3Russell
3
Jennings
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 child’s 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.
Organization and
Status of Materials:
ScIT Content
The Study:
Information Storage
Information Processing
• “What is an optical fiber and what does it do?”
Future IT
Grey = Not Available
Red = Original Format
Yellow = Revision Begun
Green = Revision Complete
Blue = Internally Reviewed
Purple = Externally Reviewed
Materials located at http://www.rpi.edu/dept/phys/ScIT
Conclusions about
Mental Models:
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.
Novice
No concept of light
carrying signal
Light just needs to be
contained (by, e.g.,
dark coating)
Fibers use mirrored
surface or other nonrefractive reflection
Use phrase “Total
Internal Reflection”
Recognize that fibers work
through refractive effect
Can explain TIR in
terms of Snell’s Law
Can explain TIR “to
someone who doesn’t know
what a sine function is.”
Expert
Photograph of Optical Fiber next to sewing
needle. The core of the fiber is 62 microns in
diameter; the cladding is 125 microns.
• Follow-up questions included “How does the fiber keep the light
from escaping?” and “What can you tell me about refraction?”
2 Physics Faculty
• Faculty, REU students, and inservice (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 WebCT’s Chat
Room in the Spring of 2003.
5
Physics
Students
(REU)
5 In-Service
Teachers
22 ScIT PreInstruction
8 ScIT PostInstruction
Demographics of Interviewees
Conclusions
about Interview Formats:
• 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”
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: can’t 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.
Laser light
trapped in a
plastic fiber. Air
serves as the
cladding.
[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 child’s 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.