Forum: Teachers Lab

Topic: Testing for Misconceptions

Topic Posted by: Sheldon Schafer (sls@bradley.bradley.edu )
Organization: Lakeview Museum Planetarium
Date Posted: Thu Feb 25 0:15:50 US/Eastern 1999

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Posted by: Sheldon Schafer (sls@bradley.edu )
Organization:Lakeview Museum Planetarium
Date posted: Thu Feb 25 0:21:40 US/Eastern 1999
Subject: Testing for Misconceptions - Survey
Message:
I took the survey, and was surprised to miss question number 1. I noticed alot of other teachers missed it too.
I'm sure I'm not the first to note this about question 1 on the survey, but responding "D" does not necessarily represent a misconception of the shape of the Earth's orbit. Rather, respondents who pick "D" may simply have a solid background in astronomy, and Kepler's Laws. My reasoning follows: Consulting "Astronomy" (Kaler), "Journey Through the Universe" (Pasachoff), "Exploration of the Universe"(Abell, Morrison & Wolff), "In Quest of the Universe" (Kuhn) and in my experience, every other text in astronomy, "D" is the diagram used in each of these to depict the elliptical nature of the Earth's orbit. True, the ellipticity is exaggerated, but then too are the size of the Earth and Sun in the diagram. Diagram "A" is clearly a "perfect" circle with the Sun at the center. Since the ellipticity of the Earth's orbit is too slight to show on the scale of a diagram such as was used, clearly "D" was exaggerated slightly (well, maybe a bit more than slightly) so the respondent would know that it was an ellipse, not a circle. Only "D" depicts Kepler's First Law - The orbits of the planets (Earth included) are ellipses with the Sun at one focus! The point is, even well intentioned diagrams can fall victim to "misconception" or misPERception. We also have to be careful that our tests which identify misconceptions are actually doing what we think they are.
 
 

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