I have summarized the diagrams of some 300 or so students (6 semesters worth) which they gave as free responses to an exam question from a GE course called Light, Sound, & Perception. Between 18% and 26% give answers which include arrows leaving their eyes. Their word descriptions, if given, are surprisingly consistent with their pictures, though the logic is rarely very complete.
The prompt: (12 pts) An alien stands in front of a full-length mirror, examining her ankle. There is a light right over the mirror illuminating her. Draw a side view, and the appropriate rays to explain the entire path of the light from the bulb, clear until she sees her ankle. •
•Be careful to describe the direction of the light with appropriate arrowheads or words.
•Identify the types of reflections where they occur (diffuse, specular). Follow any appropriate rules or laws.
•(You are not required to show the image and how it is formed, but you may do so for 2 bonus points.)
My current hypothesis is that students need to reconcile their explanation for the obvious effort it takes to notice something with the physics and the path light follows. They assume the effort causes the light paths.
I suspect that they also may not feel the need for all correct explanations for a phenomenon to agree.
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