Student Descriptions of Refraction and Optical Fibers
Fran Mateycik1, DJ Wagner1,2, JJ Rivera1, and Sybillyn Jennings3
1
Department of Physics, Rensselaer Polytechnic Institute, Troy, NY 12180
2
Department of Physics, Grove City College, Grove City, PA 16127
3
Department of PSYCHOLOGY, Russell Sage College, Troy, NY 12180
Abstract. This paper reports our research into how students describe and think about optical fibers and the physical
phenomena of refraction and total internal reflection (TIR) basic to their operation. The study was conducted as part of
the improvement and expansion of web-based materials for an innovative Rensselaer introductory physics course [1]
which examines the physics underlying information technology. As we developed the prototype module, we examined
students' understanding of the phenomena of refraction, TIR, and optical fibers through the use of clinical interviews.
As students discussed refraction and tried to explain how optical fibers work, several patterns emerged. Our analysis of
these patterns drives our assessment of the effectiveness of the revised materials in addressing students' transfer of
learning as well as the development of a multiple-choice diagnostic tool. This paper presents our categorizations of
student responses and discusses how we are modifying our materials to address these findings.
[1] Materials found at http://www.rpi.edu/dept/phys/ScIT/
INTRODUCTION
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How they describe optical fibers seems to lend
itself to the notion of a progression. When they’re
faced with trying to describe refraction, there are
multiple starting points. They look for physical images
that make sense of them (prism, straw) and try to build
up from that experience.
Optical fibers were our primary objective, and we
have been able to construct a model of student
understanding of them. Refraction was a secondary
objective, and our findings are preliminary. Time
limitations and the direction taken during the interview
determined how deeply we were able to probe this
subject.
Experts all went back to “first principles” of speed
and definition of index of refraction when explaining
TIR w/o sines. pre-experts used Snell as a starting
point and thus had difficulty explaining without sines.
Our materials start with notion of speed.
The prism experience gives rise to a sense of light
bending and being separated into colors as though
these things are undifferentiated phenomena. To come
to understand that bending and dispersion can occur
independently requires other experiences beyond the
prism.
Heinz-Werner law of orthogenetic
development.
1948
Student learning is like
unification theories – see lots of separate occurrences
and ultimately (hopefully) find patterns and
commonality.
Difficult to elicit notion of light carrying signal –
those who knew it evidently thought it was obvious
and interpreted my questioning in a different ‘light’:
S303, (DJ: What passes through the strands? S303:
data? DJ: What carries the data? tin can/string.
S303: light) But some definite non-photonic models
emerged (317).
Three pieces of information (need cognitive words
here) seem to be necessary to correctly describe how
optical fibers work:

Light must travel down an optical fiber
without spreading out or diffusing (data must
remain intact).

Mirrored surfaces will not work.

Light may be guided
phenomenon, TIR
by
a
refractive
Students espousing Stages 1 or 2 lack cognizance
of the first point – they have no concept of how
data is encoded into, and carried by, light. Students
in stages 3 A, B, and possibly C believe mirrors
can solve all their problems. Students in stage 3D
have recognized the second point above – most
connect this point to the need for flexibility.
Experts (the faculty interviewed) recognize that
point 2 is also due to the loss inherent to mirrors.
[Jim quote?] Mirrors absorb so much of the signal
that light could travel down a mirrored tube for
only xxx meters before being 90% diminished.
While interviewees were able to deduce the first
two points based on a description of what a fiber
must be able to do and/or past experience, the third
point was much more difficult to embrace without
explicit instruction. Only one of the interviewees
above stage 3 had apparently never been “told” that
fibers work through refraction. We plan to probe
this more deeply in the future by querying students
in classes that cover refraction but don’t address
the connection to fibers.
Stages 1-3 are interconnected – subjects can move
between them. But no one goes about 4A without
explicit instruction.
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ACKNOWLEDGMENTS
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2. Brown, M. P., and Austin, K., Appl. Phys. Letters 65,
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3. Wang, R.T., “Title of Chapter,” in Classic Physiques,
edited by R. B. Hamil, Publisher City: Publisher Name,
1997, pp. 212-213.
4. Smith, C. D., and Jones, E. F., “Load-Cycling in Cubic
Press” in Shock Compression in Condensed Matter-1997,
edited by S. C. Schmidt et al., AIP Conference
Proceedings 429, New York: American Institute of
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