Exploring Student Conceptions about Optical Fibers and Total

Exploring Student Conceptions about Optical Fibers and Total Internal Reflection DJ Wagner Grove City College djwagner@gcc. edu Rensselaer wagnerdj@rpi. edu

Context for this talk: Sc. IT Ø The Science of Information Technology is a course developed at Rensselaer l l Ø Goal is for technology users to appreciate phenomena behind technology and the limits of those phenomena (minimal prerequisites) Currently have NSF support to develop materials for the course so they can be used elsewhere Diagnostic exam developed for first offering in 1999 in need of revision, extension Currently working on Information Transfer unit www. rpi. edu/dept/phys/Sc. IT

My Experience Ø Threw together MC diagnostic test before first offering of Sc. IT l Ø Ø Ø Wanted to know both initial state of students and whether students learned anything Added questions on material not initially covered, reworded a few questions Recognized limits of test, started to probe student conceptions Long-answer questions introduced on diagnostic test last spring Started interviews this summer – am continuing with electronic interviews during this conference Finally looked at literature

Why assess carefully? Ø “Efforts to develop innovative curriculum consistent with findings from research do not ensure that the end product will be effective. ” • T. O'Brien Pride, S. Vokos, and L. C. Mc. Dermott 1 Ø “If I had to reduce all of educational psychology to just one principle, I would say this: The most important single factor influencing learning is what the learner already knows. Ascertain this and teach him accordingly. ” • D. P. Ausubel, in Educational Psychology: A Cognitive View, As quoted by Novak, Patterson, Gavrin, and Christian 2

My Interview Questions Ø What does an optical fiber do? Ø How does it accomplish that? Ø (If know about TIR) How would you explain the concept of total internal reflection to someone who doesn’t know what a sine function is?

Expected Results of Interviews Ø Existence of mirror-coated misconception confirmed Ø Physics majors (and physicists) have difficulty explaining concepts such as TIR without equations l S 9 transcript: • DJ: “How would you change your explanation if you were trying to explain it to somebody with no physics background? ” • S 9: “Well, I’d start out by explaining Snell’s Law, ” and go into mathematical ratios. • DJ: “What if you had somebody who didn’t understand what sines are? ” • S 9: “I guess I’d have to give a definition of sine, with right triangle and …”

Unexpected Results of Interviews Ø Prior experience understood l S 5 clip – Disney (DJ = Interviewer) S 5: Well I'm kind of thinking like those things you get at like Disney World or something with a characters head and then it's got like those little strings that come out of the top. And there's like a light that you see at the end of the strings, but the strings themselves don't look lit up. That's kind of what I'm thinking of. DJ: So is it like a metallic surface that's like reflecting it or …? S 5: Like in those I think they're plastic because their soft and you can kind of brush your hand through them. So I would imagine that it's some kind of non-metallic material.

Unexpected Results of Interviews Ø Prior experience understood l S 6 clip – fiber as filter “An optical fiber, um, I remember seeing it in a commercial once or something. And they’re describing it like whatever sound wave or whatever comes in, it kind of breaks up into its particles and this optical fiber sort of filters those particles out to make … their sight, the sound or whatever it’s trying to achieve. Optical meaning light. So I am assuming that it's light particles getting broken up and then kind of reassembled with higher resolution perhaps these fibers, you know, help create better resolution. ” Ø Learned that fiber optics may resonate with more people than optical fibers

An expected misconception seen in unexpected places The angle of refraction exceeds 90 o when TIR occurs l l Expressed by a physics major entering his junior year Asimov leaves his reader with same idea: “[light leaving water with q > qc] should emerge at an angle of more than 90 o, which means that it really does not emerge at all, since an angle of more than 90 o to the normal will direct it under water again. ” 4

Tips for Interviewers Ø Skills needed (according to Kraus) 5 l l l Ø Deep understanding of content Knowledge of research on student conceptions Asking appropriate questions Additional useful skills (my input) l l Listening skills Ability to refrain from putting words in students’ mouths Ability to communicate interest and encouragement non-verbally Time (or typists) to accomplish transcription